The Diagnosis, Evaluation and Management of von Willebrand Disease: Full Report

NHLBI von Willebrand Disease Expert Panel

Chair

William L. Nichols, Jr., M.D. (Mayo Clinic, Rochester, MN)

Members

Mae B. Hultin, M.D. (Stony Brook University, Stony Brook, NY); Andra H. James, M.D. (Duke University Medical Center, Durham, NC); Marilyn J. Manco-Johnson, M.D. (The University of Colorado at Denver and Health Sciences Center, Aurora, CO, and The Children's Hospital of Denver, CO); Robert R. Montgomery, M.D. (BloodCenter of Wisconsin and Medical College of Wisconsin, Milwaukee, WI); Thomas L. Ortel, M.D., Ph.D. (Duke University Medical Center, Durham, NC); Margaret E. Rick, M.D. (National Institutes of Health, Bethesda, MD); J. Evan Sadler, M.D., Ph.D. (Washington University, St. Louis, MO); Mark Weinstein, Ph.D. (U.S. Food and Drug Administration, Rockville, MD); Barbara P. Yawn, M.D., M.Sc. (Olmsted Medical Center and University of Minnesota, Rochester, MN)

National Institutes of Health Staff

Rebecca Link, Ph.D. (National Heart, Lung, and Blood Institute; Bethesda, MD); Sue Rogus, R.N., M.S. (National Heart, Lung, and Blood Institute, Bethesda, MD)

Staff

Ann Horton, M.S.; Margot Raphael; Carol Creech, M.I.L.S.; Elizabeth Scalia, M.I.L.S.; Heather Banks, M.A., M.A.T.; Patti Louthian (American Institutes for Research, Silver Spring, MD)

Financial and Other Disclosures

The participants who disclosed potential conflicts were Dr. Andra H. James (medical advisory panel for ZLB Behring and Bayer; NHF, MASAC), Dr. Marilyn Manco-Johnson (ZLB Behring Humate-P® Study Steering Committee and Grant Recipient, Wyeth Speaker, Bayer Advisor and Research Grant Recipient, Baxter Advisory Committee and Protein C Study Group, Novo Nordisk Advisory Committee), Dr. Robert Montgomery (Aventis Foundation Grant; GTI, Inc., VWFpp Assay; ZLB Behring and Bayer Advisory Group; NHF, MASAC), and Dr. William Nichols (Mayo Special Coagulation Laboratory serves as "central lab" for Humate-P® study by ZLB Behring). All members submitted financial disclosure forms.

Introduction

Von Willebrand disease (VWD) is an inherited bleeding disorder that is caused by deficiency or dysfunction of von Willebrand factor (VWF), a plasma protein that mediates the initial adhesion of platelets at sites of vascular injury and also binds and stabilizes blood clotting factor VIII (FVIII) in the circulation. Therefore, defects in VWF can cause bleeding by impairing platelet adhesion or by reducing the concentration of FVIII.

VWD is a relatively common cause of bleeding, but the prevalence varies considerably among studies and depends strongly on the case definition that is used. VWD prevalence has been estimated in several countries on the basis of the number of symptomatic patients seen at hemostasis centers, and the values range from roughly 23 to 110 per million population (0.0023 to 0.01 percent).1

The prevalence of VWD also has been estimated by screening populations to identify persons with bleeding symptoms, low VWF levels, and similarly affected family members. This population-based approach has yielded estimates for VWD prevalence of 0.6 percent,2 0.8 percent,3 and 1.3 percent4—more than two orders of magnitude higher than the values arrived at by surveys of hemostasis centers.

The discrepancies between the methods for estimating VWD prevalence illustrate the need for better information concerning the relationship between VWF levels and bleeding. Many bleeding symptoms are exacerbated by defects in VWF, but the magnitude of the effect is not known. For example, approximately 12 percent of women who have menstrual periods have excessive menstrual bleeding.5 This fraction is much higher among women who have VWD, but it also appears to be increased for women who have VWF levels at the lower end of the normal range. Quantitative data on these issues would allow a more informed approach to the diagnosis and management of VWD and could have significant implications for medical practice and for public health.

Aside from needs for better information about VWD prevalence and the relationship of low VWF levels to bleeding symptoms or risk, there are needs for enhancing knowledge and improving clinical and laboratory diagnostic tools for VWD. Furthermore, there are needs for better knowledge of and treatment options for management of VWD and bleeding or bleeding risk. As documented in this VWD guidelines publication, a relative paucity of published studies is available to support some of the recommendations which, therefore, are mainly based on Expert Panel opinion.

Guidelines for VWD diagnosis and management, based on the evidence from published studies and/or the opinions of experts, have been published for practitioners in Canada,6 Italy,7 and the United Kingdom,8,9 but not in the United States. The VWD guidelines from the U.S. Expert Panel are based on review of published evidence as well as expert opinion. Users of these guidelines should be aware that individual professional judgment is not abrogated by recommendations in these guidelines.

These guidelines for diagnosis and management of VWD were developed for practicing primary care and specialist clinicians—including family physicians, internists, obstetrician-gynecologists, pediatricians, and nurse-practitioners—as well as hematologists and laboratory medicine specialists.

History of This Project

During the spring of 2004, the National Heart, Lung, and Blood Institute (NHLBI) began planning for the development of clinical practice guidelines for VWD in response to the FY 2004 appropriations conference committee report (House Report 108-401) recommendation. In that report, the conferees urged NHLBI to develop a set of treatment guidelines for VWD and to work with medical associations and experts in the field when developing such guidelines. In consultation with the American Society of Hematology (ASH), the Institute convened an Expert Panel on VWD, chaired by Dr. William Nichols of the Mayo Clinic, Rochester, MN. The Expert Panel members were selected to provide expertise in basic sciences, clinical and laboratory diagnosis, evidence-based medicine, and the clinical management of VWD, including specialists in hematology as well as in family medicine, obstetrics and gynecology, pediatrics, internal medicine, and laboratory sciences. The Expert Panel comprised one basic scientist and nine physicians—including one family physician, one obstetrician and gynecologist, and seven hematologists with expertise in VWD (two were pediatric hematologists). Ad hoc members of the Panel represented the Division of Blood Diseases and Resources of the NHLBI. The Panel was coordinated by the Division for the Application of Research Discoveries (DARD), formerly the Office of Prevention, Education, and Control of the NHLBI. Panel members disclosed, verbally and in writing, any financial conflicts. (See financial and other disclosure summaries.)

Charge to the Panel

Dr. Barbara Alving, then Acting Director of the NHLBI, gave the charge to the Expert Panel to examine the current science in the area of VWD and to come to consensus regarding clinical recommendations for diagnosis, treatment, and management of this common inherited bleeding disorder. The Panel was also charged to base each recommendation on the current science and to indicate the strength of the relevant literature for each recommendation.

The development of this report was entirely funded by the NHLBI, National Institutes of Health (NIH). Panel members and reviewers participated as volunteers and were reimbursed only for travel expenses related to the three in-person Expert Panel meetings.

Panel Assignments

After the Expert Panel finalized a basic outline for the guidelines, members were assigned to the three sections: (1) Introduction and Background, (2) Diagnosis and Evaluation, and (3) Management of VWD. Three members were assigned lead responsibility for a particular section. The section groups were responsible for developing detailed outlines for the sections, reviewing the pertinent literature, writing the sections, and drafting recommendations with the supporting evidence for the full Panel to review.

Literature Searches

Three section outlines, approved by the Expert Panel chair, were used as the basis for compiling relevant search terms, using the Medical Subject Headings (MeSH terms) of the MEDLINE database. If appropriate terms were not available in MeSH, then relevant non-MeSH keywords were used. In addition to the search terms, inclusion and exclusion criteria were defined based on feedback from the Panel about specific limits to include in the search strategies, specifically:

• Date restriction: 1990-2004
• Language: English
• Study/publication types: randomized-controlled trial; meta-analysis; controlled clinical trial; epidemiologic studies; prospective studies; multicenter study; clinical trial; evaluation studies; practice guideline; review, academic; review, multicase; technical report; validation studies; review of reported cases; case reports; journal article (to exclude letters, editorials, news, etc.)

The search strategies were constructed and executed in the MEDLINE database as well as in the Cochrane Database of Systematic Reviews to compile a set of citations and abstracts for each section. Initial searches on specific keyword combinations and date and language limits were further refined by using the publication type limits to produce results that more closely matched the section outlines. Once the section results were compiled, the results were put in priority order by study type as follows:

1. Randomized-controlled trial
2. Meta-analysis (quantitative summary combining results of independent studies)
3. Controlled clinical trial
4. Multicenter study
5. Clinical trial (includes all types and phases of clinical trials)
6. Evaluation studies
7. Practice guideline (for specific health care guidelines)
8. Epidemiological
9. Prospective studies
10. Review, academic (comprehensive, critical, or analytical review)
11. Review, multicase (review with epidemiological applications)
12. Technical report
13. Validation studies
14. Review of reported cases (review of known cases of a disease)
15. Case reports

Upon examination of the yield of the initial literature search, it was determined that important areas in the section outlines were not addressed by the citations, possibly due to the date exclusions. In addition, Panel members identified pertinent references from their own searches and databases, including landmark references predating the 1990 date restriction, and 2005 and 2006 references (to October 2006). Therefore, as a followup, additional database searching was done using the same search strategies from the initial round, but covering dates prior to 1990 and during 2005 and 2006 to double check for key studies appearing in the literature outside the limits of the original range of dates. Also, refined searches in the 1990-2006 date range were conducted to analyze the references used by Panel members that had not appeared in the original search results.

These revised searches helped round out the database search to provide the most comprehensive approach possible. As a result, the references used in the guidelines included those retrieved from the two literature searches combined with the references suggested by the Panel members. These references inform the guidelines and clinical recommendations, based on the best available evidence in combination with the Panel's expertise and consensus.

Clinical Recommendations—Grading and Levels of Evidence

Recommendations made in this document are based on the levels of evidence described in Table 1, with a priority grading system of A, B, or C. Grade A is reserved for recommendations based on evidence levels Ia and Ib. Grade B is given for recommendations having evidence levels of IIa, IIb, and III; and Grade C is for recommendations based on evidence level IV.8 None of the recommendations merited a Grade of A. Evidence tables are provided at the end of the document for those recommendations that are graded as B and have two or more references

Table 1. Level of Evidence

Source: Acute pain management: operative or medical procedures and trauma. (Clinical practice guideline). Publication No. AHCPR 92-0032. Rockville, MD: Agency for Health Care Policy and Research, Public Health Service, U.S. Department of Health and Human Services, February 1992.

External and Internal Review

The NHLBI sought outside review of the guidelines through a two-fold process. The following Government agencies and professional organizations were invited to review the draft document and submit comments: Centers for Disease Control and Prevention, Food and Drug Administration, American Academy of Family Physicians, American College of Obstetricians and Gynecologists, American College of Physicians, American Society of Hematology, American Society of Pediatric Hematology/Oncology, College of American Pathologists, Hemophilia & Thrombosis Research Society, National Hemophilia Foundation Medical and Scientific Advisory Committee, and the North American Specialized Coagulation Laboratory Association. In addition, the guidelines were posted on the NHLBI Web site for public review and comment during a 30-day period ending September 22, 2006. Comments from the external review were compiled and given to the full Panel for review and consensus. Revisions to the document were then made as appropriate. The final draft, after Panel approval, was sent through review within the NIH and finally approved for publication by the NHLBI Director.

Discovery and Identification of VWD/VWF

The patient who led to the discovery of a hereditary bleeding disorder that we now call VWD was a 5-year-old girl who lived on the Åland Islands and was brought to Deaconess Hospital in Helsinki, Finland, in 1924 to be seen by Dr. Erik von Willebrand.10 He ultimately assessed 66 members of her family and reported in 1926 that this was a previously undescribed bleeding disorder that differed from hemophilia and exhibited (1) mucocutaneous bleeding, (2) autosomal inheritance rather than being linked to the X chromosome, (3) prolonged bleeding times by the Duke method (ear lobe bleeding time), and (4) normal clotting time. Not only did he recognize the autosomal inheritance pattern, but he recognized that bleeding symptoms were greater in children and in women of childbearing age. He subsequently found that blood transfusions were useful not only to correct the anemia but also to control bleeding.

In the 1950s, it became clear that a "plasma factor," antihemophilic factor (FVIII), was decreased in these persons and that Cohn fraction I-0 could correct both the plasma deficiency of FVIII and the prolonged bleeding time. For the first time, the factor causing the long bleeding time was called "von Willebrand factor." As cryoprecipitate and commercial FVIII concentrates were developed, it was recognized that both VWF and "antihemophilic factor" (FVIII) purified together.

When immunoassays were developed, persons who had VWD (in contrast to those who had hemophilia A) were found to have reduced "factor VIII-related antigen" (FVIIIR:Ag), which we now refer to as VWF:Ag. Characterization of the proteins revealed that FVIII was the clotting protein deficient in hemophilia A, and VWF was a separate "FVIII carrier protein" that resulted in the cofractionation of both proteins in commercial concentrates. Furthermore, a deficiency of VWF resulted in increased FVIII clearance because of the reduced carrier protein, VWF. Since the 1980s, molecular and cellular studies have defined hemophilia A and VWD more precisely. Persons who had VWD had a normal FVIII gene on the X chromosome, and some were found to have an abnormal VWF gene on chromosome 12. Variant forms of VWF were recognized in the 1970s, and we now recognize that these variations are the result of synthesis of an abnormal protein. Gene sequencing identified many of these persons as having a VWF gene mutation. The genetic causes of milder forms of low VWF are still under investigation, and these forms may not always be caused by an abnormal VWF gene. In addition, there are acquired disorders that may result in reduced or dysfunctional VWF (see section on "Acquired von Willebrand Syndrome" [AVWS]). Table 2 contains a synopsis of VWF designations, functions, and assays. Table 3 contains abbreviations used throughout this document.

Table 2. Synopsis of VWF Designations, Properties, and Assays

*See Table 3. Nomenclature and Abbreviations.

The VWF Protein and Its Functions In Vivo

VWF is synthesized in two cell types. In the vascular endothelium, VWF is synthesized and subsequently stored in secretory granules (Weibel-Palade bodies) from which it can be released by stress or drugs such as desmopressin (DDAVP, 1-desamino-8-D-arginine vasopressin), a synthetic analog of vasopressin. VWF is also synthesized in bone marrow megakaryocytes where it is stored in platelet alpha-granules from which it is released following platelet activation. DDAVP does not release platelet VWF.

VWF is a protein that is assembled from identical subunits into linear strings of varying size referred to as multimers. These multimers can be >20 million daltons in mass and >2 micrometers in length. The complex cellular processing consists of dimerization in the endoplasmic reticulum (ER), glycosylation in the ER and Golgi, multimerization in the Golgi, and packaging into storage granules. The latter two processes are under the control of the VWF propeptide (VWFpp), which is cleaved from VWF at the time of storage. VWF that is released acutely into the circulation is accompanied by a parallel rise in FVIII, but it is still not entirely clear whether this protein-protein association first occurs within the endothelial cell.11,12

In plasma, the FVIII-VWF complex circulates as a loosely coiled protein complex that does not interact strongly with platelets or endothelial cells under basal conditions. When vascular injury occurs, VWF becomes tethered to the exposed subendothelium (collagen, etc.). The high fluid shear rates that occur in the microcirculation appear to induce a conformational change in multimeric VWF that causes platelets to adhere, become activated, and then aggregate so as to present an activated platelet phospholipid surface. This facilitates clotting that is, in part, regulated by FVIII. Because of the specific characteristics of hemostasis and fibrinolysis on mucosal surfaces, symptoms in VWD are often greater in these tissues.

Plasma VWF is primarily derived from endothelial synthesis. Platelet and endothelial cell VWF are released locally following cellular activation where this VWF participates in the developing hemostatic plug or thrombus (see Figure 1).

Plasma VWF has a half-life of approximately 12 hours (range 9-15 hours). VWF is present as very large multimers that are subjected to physiologic degradation by the metalloprotease ADAMTS13 (A Disintegrin-like And Metalloprotease domain [reprolysin type] with Thrombospondin type I motifs). Deficiency of ADAMTS13 is associated with the pathologic microangiopathy of thrombotic thrombocytopenic purpura (TTP). The most common variant forms of type 2A VWD are characterized by increased VWF susceptibility to ADAMTS13.

Table 3. Nomenclature and Abbreviations

*These abbreviations (for FVIII and VWF and all their properties) are defined in Marder VJ, Mannucci PM, Firkin BG, Hoyer LW, Meyer D. Standard nomenclature for factor VIII and von Willebrand factor: a recommendation by the International Committee on Thrombosis and Haemostasis. Thromb Haemost 1985 Dec;54(4):871-872; Mazurier C, Rodeghiero F. Recommended abbreviations for von Willebrand Factor and its activities. Thromb Haemost 2001 Aug;86(2):712.

Factors that affect levels of plasma VWF include age, race, ABO and Lewis blood groups, epinephrine, inflammatory mediators, and endocrine hormones (particularly those associated with the menstrual cycle and pregnancy). VWF is increased during pregnancy (a three- to fivefold elevation over the woman's baseline by the third trimester), with aging, and with acute stress or inflammation. Africans and African Americans have higher average levels of VWF than the Caucasian population.13,14 VWF is reduced by hypothyroidism and rarely by autoantibodies to VWF. The rate of VWF synthesis probably is not affected by blood group; however, the survival of VWF appears to be reduced in individuals who have type O blood. In fact, ABO blood group substance has been identified on VWF.

The Genetics of VWDM

Since the 1980s, molecular and cellular studies have defined hemophilia A and VWD more precisely. Persons who have severe VWD have a normal FVIII gene on the X chromosome, and some are found to have an abnormal VWF gene on chromosome 12. The VWF gene is located near the tip of the short arm of chromosome 12, at 12p13.3.15 It spans approximately 178 kb of DNA and contains 52 exons.16 Intron-exon boundaries tend to delimit structural domains in the protein, and introns often occur at similar positions within the gene segments that encode homologous domains. Thus, the structure of the VWF gene reflects the mosaic nature of the protein (Figure 2).

A partial, unprocessed VWF pseudogene is located at chromosome 22q11.2.17 This pseudogene spans approximately 25 kb of DNA and corresponds to exons 23-34 and part of the adjacent introns of the VWF gene.18 This segment of the gene encodes domains A1A2A3, which contain binding sites for platelet glycoprotein Ib (GPIb) and collagen, as well as the site cleaved by ADAMTS13. The VWF pseudogene and gene have diverged 3.1 percent in DNA sequence, consistent with a relatively recent origin of the pseudogene by partial gene duplication.18 This pseudogene is found in humans and great apes (bonobo, chimpanzee, gorilla, orangutan) but not in more distantly related primates.19 The VWF pseudogene complicates the detection of VWF gene mutations because polymerase chain reactions (PCRs) can inadvertently amplify segments from either or both loci, but this difficulty can be overcome by careful design of gene-specific PCR primers.18

Figure 1. VWF and Normal Hemostasis

A cross-sectioned blood vessel shows stages of hemostasis. Top, VWF is the carrier protein for blood clotting factor VIII (FVIII). Under normal conditions VWF does not interact with platelets or the blood vessel wall that is covered with endothelial cells. Middle left, following vascular injury, VWF adheres to the exposed subendothelial matrix. Middle right, after VWF is uncoiled by local shear forces, platelets adhere to the altered VWF and these platelets undergo activation and recruit other platelets to this injury site. Bottom left, the activated and aggregated platelets alter their membrane phospholipids exposing phosphatidylserine, and this activated platelet surface binds clotting factors from circulating blood and initiates blood clotting on this surface where fibrin is locally deposited. Bottom right, the combination of clotting and platelet aggregation and adhesion forms a platelet-fibrin plug, which results in the cessation of bleeding. The extent of the clotting is carefully regulated by natural anticoagulants. Subsequently, thrombolysis initiates tissue repair and ultimately the vessel may be re-endothelialized and blood flow maintained. 
Note: Used by permission of R.R. Montgomery.

The VWF pseudogene may occasionally serve as a reservoir of mutations that can be introduced into the VWF locus. For example, some silent and some potentially pathogenic mutations have been identified in exons 27 and 28 of the VWF gene of persons who have VWD. These same sequence variations occur consecutively in the VWF pseudogene and might have been transferred to the VWF by gene conversion.20-22 The segments involved in the potential gene conversion events are relatively short, from a minimum of 7 nucleotides20 to a maximum of 385 nucleotides.22 The frequency of these potential interchromosomal exchanges is unknown.

The spectrum of VWF gene mutations that cause VWD is similar to that of many other human genetic diseases and includes large deletions, frameshifts from small insertions or deletions, splice-site mutations, nonsense mutations causing premature termination of translation, and missense mutations affecting single amino acid residues. A database of VWF mutations and polymorphisms has been compiled for the International Society on Thrombosis and Haemostasis (ISTH)23,24 and is maintained for online access at the University of Sheffield (http://www.shef.ac.uk/vwf/index.html). (link is external) Mutations causing VWD have been identified throughout the VWF gene. In contrast to hemophilia A, in which a single major gene rearrangement causes a large fraction of severe disease, no such recurring mutation is common in VWD. There is a good correlation between the location of mutations in the VWF gene and the subtype of VWD, as discussed in more detail in "Classification of VWD Subtypes." In selected families, this information can facilitate the search for VWF mutations by DNA sequencing.

Figure 2. Structure and Domains of VWF

The von Willebrand factor (VWF) protein sequence (amino acid 1-2813) is aligned with the cDNA sequence (nucleic acid 1-8439). The VWF signal peptide is the first 22 aa, the propeptide (VWFpp) aa 23-763, and mature VWF aa 764-2800. Type 2 mutations are primarily located in specific domains (regions) along the VWF protein. Types 2A, 2B, and 2M VWF mutations are primarily located within exon 28 that encodes for the A1 and A2 domains of VWF. The two different types of 2A are those that have increased proteolysis (2A2) and those with abnormal multimer synthesis (2A1). Type 2N mutations are located within the D? and D3 domains. Ligands that bind to certain VWF domains are identified, including FVIII, heparin, GPIb (platelet glycoprotein Ib complex), collagen, and GPIIb/IIIa (platelet glycoprotein IIb/IIIa complex that binds to the RGD [arginine-glycine-aspartate] amino acid sequence in VWF). 
Note: Used by permission of R.R. Montgomery.

Classification of VWD Subtypes

VWD is classified on the basis of criteria developed by the VWF Subcommittee of the ISTH, first published in 1994 and revised in 2006 (Table 4).25,26

The classification was intended to be clinically relevant to the treatment of VWD. Diagnostic categories were defined that encompassed distinct pathophysiologic mechanisms and correlated with the response to treatment with DDAVP or blood products. The classification was designed to be conceptually independent of specific laboratory testing procedures, although most of the VWD subtypes could be assigned by using tests that were widely available. The 1994 classification reserved the designation of VWD for disorders caused by mutations within the VWF gene,25 but this criterion has been dropped from the 2006 classification26 because in practice it is verifiable for only a small fraction of patients.

VWD is classified into three major categories: partial quantitative deficiency (type 1), qualitative deficiency (type 2), and total deficiency (type 3). Type 2 VWD is divided further into four variants (2A, 2B, 2M, 2N) on the basis of details of the phenotype. Before the publication of the 1994 revised classification of VWD,25 VWD subtypes were classified using Roman numerals (types I, II, and III), generally corresponding to types 1, 2, and 3 in the 1994 classification, and within type II several subtypes existed (designated by adding sequential letters of the alphabet; i.e., II-A through II-I). Most of the latter VWD variants were amalgamated as type 2A in the 1994 classification, with the exception of type 2B (formerly II-B) for which a separate new classification was created. In addition, a new subtype (2M) was created to include variants with decreased platelet dependent function (VWF:RCo) but no significant decrease of higher molecular weight VWF multimers (which may or may not have other aberrant structure), with "M" representing "multimer." Subtype 2N VWD was defined, with "N" representing "Normandy" where the first individuals were identified, with decreased FVIII due to VWF defects of FVIII binding.

Type 1 VWD affects approximately 75 percent of symptomatic persons who have VWD (see Castaman et al., 2003 for a review).27 Almost all of the remaining persons are divided among the four type 2 variants, and the partitioning among them varies considerably among centers. In France, for example, patients’ distribution was reported to be 30 percent type 2A, 28 percent type 2B, 8 percent type 2M (or unclassified), and 34 percent type 2N.28 In Bonn, Germany, the distribution was reported to be 74 percent type 2A, 10 percent type 2B, 13 percent type 2M, and 3.5 percent type 2N.29Table 5 summarizes information about inheritance, prevalence, and bleeding propensity in persons who have different types of VWD.

Table 4. Classification of VWD

Note: VWD types are defined as described in Sadler JE, Budde U, Eikenboom JC, Favaloro EJ, Hill FG, Holmberg L, Ingerslev J, Lee CA, Lillicrap D, Mannucci PM, et al. Update on the pathophysiology and classification of von Willebrand disease: a report of the Subcommittee on von Willebrand Factor. J Thromb Haemost 2006 Oct;4(10):2103-2114.

Table 5. Inheritance, Prevalence, and Bleeding Propensity in Patients Who Have VWD

The prevalence of type 3 VWD in the population is not known precisely but has been estimated (per million population) as: 0.55 for Italy,30 1.38 for North America,31 3.12 for Sweden,30 and 3.2 for Israel.32 The prevalence may be as high as 6 per million where consanguinity is common.1

Type 1 VWD

Type 1 VWD is found in persons who have partial quantitative deficiency of VWF. The level of VWF in plasma is low, and the remaining VWF mediates platelet adhesion normally and binds FVIII normally. Laboratory evaluation shows concordant decreases in VWF protein concentration (VWF:Ag) and assays of VWF function (VWF:RCo). Levels of blood clotting FVIII usually parallel VWF and may be reduced secondary to reduced VWF. Usually, in type 1 VWD, the FVIII/VWF:Ag ratio is 1.5-2.0. In most persons who have type 1 VWD, this results in FVIII being normal, or mildly decreased, and not reduced as much as the VWF. VWF multimer gels show no significant decrease in large VWF multimers.25 The laboratory evaluation of VWD is discussed in the "Diagnosis and Evaluation" section.

The spectrum of mutations occurring in VWD type 1 has been described extensively in two major studies.33,34 Particularly severe, highly penetrant forms of type 1 VWD may be caused by dominant VWF mutations that interfere with the intracellular transport of dimeric proVWF35-39 or that promote the rapid clearance of VWF from the circulation.38,40,41 Persons who have such mutations usually have VWF levels <20 IU/dL.33,34 Most of the mutations characterized to date cause single amino acid substitutions in domain D3.35-37,39,42 One mutation associated with rapid clearance has been reported in domain D4.38

Increased clearance of VWF from the circulation in type 1 VWD may account for the exaggerated but unexpectedly brief responses to DDAVP observed in some patients. Consequently, better data on the prevalence of increased clearance could affect the approach to diagnosing type 1 VWD and the choice of treatment for bleeding.

A diagnosis of type 1 VWD is harder to establish when the VWF level is not markedly low but instead is near the lower end of the normal range. Type 1 VWD lacks a qualitative criterion by which it can be recognized and instead relies only on quantitative decrements of protein concentration and function. VWF levels in the healthy population span a wide range of values. The mean level of plasma VWF is 100 IU/dL, and approximately 95 percent of plasma VWF levels lie between 50 and 200 IU/dL.43,44 Because mild bleeding symptoms are very common in the healthy population, the association of bleeding symptoms with a moderately low VWF level may be coincidental.45 The conceptual and practical issues associated with the evaluation of moderately low VWF levels are discussed more completely later in this section. (See "Type 1 VWD Versus Low VWF: VWF Level as a Risk Factor for Bleeding.")

Type 2 VWD

The clinical features of several type 2 VWD variants are distinct from those of type 1 VWD, and they can have strikingly distinct and specific therapeutic needs. As a consequence, the medical care of patients who have type 2 VWD benefits from the participation of a hematologist who has expertise in hemostasis. Bleeding symptoms in type 2 VWD are often thought to be more severe than in type 1 VWD, although this impression needs to be evaluated in suitable clinical studies.

Type 2A VWD refers to qualitative variants in which VWF-dependent platelet adhesion is decreased because the proportion of large VWF multimers is decreased. Levels of VWF:Ag and FVIII may be normal or modestly decreased, but VWF function is abnormal as shown by markedly decreased VWF:RCo.46 Type 2A VWD may be caused by mutations that interfere with the assembly or secretion of large multimers or by mutations that increase the susceptibility of VWF multimers to proteolytic degradation in the circulation.47-49 The deficit of large multimers predisposes persons to bleed.

The location of type 2A VWD mutations sometimes can be inferred from high-resolution VWF multimer gels. For example, mutations that primarily reduce multimer assembly lead to the secretion of multimers that are too small to engage platelets effectively and therefore are relatively resistant to proteolysis by ADAMTS13. Homozygous mutations in the propeptide impair multimer assembly in the Golgi and give rise to a characteristic "clean" pattern of small multimers that lack the satellite bands usually associated with proteolysis (see "Diagnosis and Evaluation"); this pattern was initially described as "type IIC" VWD.50-52 Heterozygous mutations in the cystine knot (CK) domain can impair dimerization of proVWF in the ER and cause a recognizable multimer pattern originally referred to as "type IID."53,54 A mixture of monomers and dimers arrives in the Golgi, where the incorporation of monomers at the end of a multimer prevents further elongation. As a result, the secreted small multimers contain minor species with an odd number of subunits that appear as faint bands between the usual species that contain an even number of subunits. Heterozygous mutations in cysteine residues of the D3 domain also can impair multimer assembly, but these mutations often also produce an indistinct or "smeary" multimer pattern referred to as "type IIE."55,56

In contrast to mutations that primarily affect multimer assembly, mutations within or near the A2 domain of VWF cause type 2A VWD that is associated with markedly increased proteolysis of the VWF subunits56 (see Figure 2). These mutations apparently interfere with the folding of the A2 domain and make the Tyr1605-Met1606 bond accessible to ADAMTS13 even in the absence of increased fluid shear stress. Two subgroups of this pattern have been distinguished: group I mutations enhance proteolysis by ADAMTS13 and also impair multimer assembly, whereas group II mutations enhance proteolysis without decreasing the assembly of large VWF multimers.49 Computer modeling of domain A2 suggests that group I mutations affect both assembly and proteolysis, because group I mutations have a more disruptive effect on the folding of domain A2 than do group II mutations.57

Type 2B VWD is caused by mutations that pathologically increase platelet-VWF binding, which leads to the proteolytic degradation and depletion of large, functional VWF multimers.56,58 Circulating platelets also are coated with mutant VWF, which may prevent the platelets from adhering at sites of injury.59

Although laboratory results for type 2B VWD may be similar to those in type 2A or type 2M VWD, patients who have type 2B VWD typically have thrombocytopenia that is exacerbated by surgery, pregnancy, or other stress.60-62 The thrombocytopenia probably is caused by reversible sequestration of VWF-platelet aggregates in the microcirculation. These aggregates are dissolved by the action of ADAMTS13 on VWF, causing the characteristic decrease of large VWF multimers and the prominent satellite banding pattern that indicates increased proteolytic degradation.63,64 The diagnosis of type 2B VWD depends on finding abnormally increased ristocetin induced platelet aggregation (RIPA) at low concentrations of ristocetin.

Type 2B VWD mutations occur within or adjacent to VWF domain A1,23,55,65-68 which changes conformation when it binds to platelet GPIb.69 The mutations appear to enhance platelet binding by stabilizing the bound conformation of domain A1.

Type 2M VWD includes variants with decreased VWF-dependent platelet adhesion that is not caused by the absence of high-molecular-weight VWF multimers. Instead, type 2M VWD mutations reduce the interaction of VWF with platelet GPIb or with connective tissue and do not substantially impair multimer assembly. Screening laboratory results in type 2M VWD and type 2A VWD are similar, and the distinction between them depends on multimer gel electrophoresis.67

Mutations in type 2M VWD have been identified in domain A1 (see Figure 2), where they interfere with binding to platelet GPIb.23,55,67,70-72 One family has been reported in which a mutation in VWF domain A3 reduces VWF binding to collagen, thereby reducing platelet adhesion and possibly causing type 2M VWD.73

Type 2N VWD is caused by VWF mutations that impair binding to FVIII, lowering FVIII levels so that type 2N VWD masquerades as an autosomal recessive form of hemophilia A.74-76 In typical cases, the FVIII level is less than 10 percent, with a normal VWF:Ag and VWF:RCo. Discrimination from hemophilia A may require assays of FVIII-VWF binding.77,78

Most mutations that cause type 2N VWD occur within the FVIII binding site of VWF (see Figure 2), which lies between residues Ser764 and Arg1035 and spans domain D? and part of domain D3.23,79,80 The most common mutation, Arg854Gln, has a relatively mild effect on FVIII binding and tends to cause a less severe type 2N VWD phenotype.77 Some mutations in the D3 domain C-terminal of Arg1035 can reduce FVIII binding,81-83 presumably through an indirect effect on the structure or accessibility of the binding site.

Type 3 VWD

Type 3 VWD is characterized by undetectable VWF protein and activity, and FVIII levels usually are very low (1-9 IU/dL).84-86 Nonsense and frameshift mutations commonly cause type 3 VWD, although large deletions, splice-site mutations, and missense mutations also can do so. Mutations are distributed throughout the VWF gene, and most are unique to the family in which they were first identified.23,87,88

A small fraction of patients who have type 3 VWD develop alloantibodies to VWF in response to the transfusion of plasma products. These antibodies have been reported in 2.6-9.5 percent of patients who have type 3 VWD, as determined by physician surveys or screening.85,89 The true incidence is uncertain, however, because of unavoidable selection bias in these studies. Anti-VWF alloantibodies can inhibit the hemostatic effect of blood-product therapy and also may cause life-threatening allergic reactions.85,90 Large deletions in the VWF gene may predispose patients to this complication.89

VWD Classification, General Issues

The principal difficulties in using the current VWD classification concern how to define the boundaries between the various subtypes through laboratory testing. In addition, some mutations have pleiotropic effects on VWF structure and function, and some persons are compound heterozygous for mutations that cause VWD by different mechanisms. This heterogeneity can produce complex phenotypes that are difficult to categorize. Clinical studies of the relationship between VWD genotype and clinical phenotype would be helpful to improve the management of patients with the different subtypes of VWD.

The distinction between quantitative (type 1) and qualitative (type 2) defects depends on the ability to recognize discrepancies among VWF assay results,80,91 as discussed in "Diagnosis and Evaluation." Similarly, distinguishing between type 2A and type 2M VWD requires multimer gel analysis. Standards need to be established for using laboratory tests to make these important distinctions.

The example of Vicenza VWD illustrates some of these problems. Vicenza VWD was first described as a variant of VWD in which the level of plasma VWF is usually <15 IU/dL and the VWF multimers are even larger than normal, like the ultralarge multimers characteristic of platelet VWF.92 The low level of VWF in plasma in Vicenza VWD appears to be explained by the effect of a specific mutation, Arg1205His, that promotes clearance of VWF from the circulation about fivefold more rapidly than normal.41 Because the newly synthesized multimers have less opportunity to be cleaved by ADAMTS13 before they are cleared, accelerated clearance alone may account for the increased multimer size in Vicenza VWD.93 Whether Vicenza VWD is classified under type 1 VWD or type 2M VWD depends on the interpretation of laboratory test results. The abnormally large multimers and very low RIPA values have led some investigators to prefer the designation of type 2M VWD.94 However, the VWF:RCo/VWF: Ag ratio typically is normal, and large VWF multimers are not decreased relative to smaller multimers, so that other investigators have classified Vicenza VWD under type 1 VWD.41 Regardless of how this variant is classified, the markedly shortened half-life of plasma VWF in Vicenza VWD is a key fact that, depending on the clinical circumstance, may dictate whether the patient should receive treatment with DDAVP or FVIII/VWF concentrates.

Type 1 VWD Versus Low VWF: VWF Level as a Risk Factor for Bleeding

Persons who have very low VWF levels, <20 IU/dL, are likely to have VWF gene mutations, significant bleeding symptoms, and a strongly positive family history.33,34,37,95-99 Diagnosing such persons as having type 1 VWD seems appropriate because they may benefit from changes in lifestyle and from specific treatments to prevent or control bleeding. Identification of affected family members also may be useful, and genetic counseling is simplified when the pattern of inheritance is straightforward.

On the other hand, VWF levels of 30-50 IU/dL, just below the usual normal range (50-200 IU/dL), pose problems for diagnosis and treatment. Among the total U.S. population of approximately 300 million, VWF levels <50 IU/dL are expected in about 7.5 million persons, who therefore would be at risk for a diagnosis of type 1 VWD. Because of the strong influence of ABO blood group on VWF level,43 about 80 percent of U.S. residents who have low VWF also have blood type O. Furthermore, moderately low VWF levels and bleeding symptoms generally are not coinherited within families and are not strongly associated with intragenic VWF mutations.100-102 In a recent Canadian study of 155 families who had type 1 VWD, the proportion showing linkage to the VWF locus was just 41 percent.98 In a similar European study, linkage to the VWF locus depended on the severity of the phenotype. If plasma levels of VWF were <30 IU/dL, linkage was consistently observed, but if levels of VWF were >30 IU/dL, the proportion of linkage was only 51 percent.97 Furthermore, bleeding symptoms were not significantly linked to the VWF gene in these families.97

Family studies suggest that 25-32 percent of the variance in plasma VWF is heritable.103,104 Twin studies have reported greater heritability of 66-75 percent,105,106 although these values may be overestimates because of shared environmental factors.104,107 Therefore, it appears that, at least in the healthy population, a substantial fraction of the variation in VWF level is not heritable.

Few genes have been identified that contribute to the limited heritability of VWF level. The major genetic influence on VWF level is ABO blood group, which is thought to account for 20-30 percent of its heritable variance.13,106,108 The mean VWF level for blood type O is 75 U/dL, which is 25-35 U/dL lower than other ABO types, and 95 percent of VWF levels for type O blood donors are between 36 and 157 U/dL.43 The Secretor locus has a smaller effect. Secretor-null persons have VWF levels slightly lower than Secretors.109

Table 6. Bleeding and VWF Level in Type 3 VWD Heterozygotes

An effect of the VWF locus has been difficult to discern by linkage analysis. One study suggested that 20 percent of the variance in VWF levels is attributable to the VWF gene,108 whereas another study could not demonstrate such a relationship.110

In sum, known genetic factors account for a minority of the heritable variation in VWF level, and moderately low VWF levels (30-50 IU/dL) do not show consistent linkage to the VWF locus.97,98,100,101 The diagnosis and management of VWD would be facilitated by better knowledge of how inherited and environmental factors influence the plasma concentration of VWF.

The attribution of bleeding to a low VWF level can be difficult because mild bleeding symptoms are very common, as discussed in the section on "Diagnosis and Evaluation" and the risk of bleeding is only modestly increased for persons who have moderately decreased VWF levels.45 For example, in the course of investigating patients who have type 3 VWD, approximately 190 obligate heterozygous relatives have had bleeding histories obtained and VWF levels measured (see Table 6). The geometric mean VWF level was 47 IU/dL,45 with a range (±2 SD) of 16-140 IU/dL. Among 117 persons who had VWF <50 IU/dL, 31 (26 percent) had bleeding symptoms. Among 74 persons who had VWF >50 IU/dL, 10 (14 percent) had bleeding symptoms. Therefore, the relative risk of bleeding was 1.9 (P = 0.046, Fisher's exact test) for persons who had low VWF. There was a trend for an increased frequency of bleeding symptoms at the lowest VWF levels: among 31 persons who had VWF levels <30 IU/dL, 12 (39 percent) had symptoms. Bleeding was mild and consisted of epistaxis, bruising, menorrhagia, and bleeding after tooth extraction. The one person who experienced postoperative bleeding had a VWF level >50 IU/dL.113

The management of bleeding associated with VWF deficiency would be facilitated by better understanding of the heritability of low VWF levels (in the range of 20-50 IU/dL), their association with intragenic VWF mutations, and their interactions with other modifiers of bleeding risk. Such data could provide a foundation for treating VWF level as a biomarker for a moderate risk of bleeding, much as high blood pressure and high cholesterol are treated as biomarkers for cardiovascular disease (CVD) risk.

Acquired von Willebrand Syndrome

Acquired von Willebrand syndrome (AVWS) refers to defects in VWF concentration, structure, or function that are not inherited directly but are consequences of other medical disorders. Laboratory findings in AVWS are similar to those in VWD and may include decreased values for VWF:Ag, VWF:RCo, or FVIII. The VWF multimer distribution may be normal, but the distribution often shows a decrease in large multimers similar to that seen in type 2A VWD.117,118 AVWS usually is caused by one of three mechanisms: autoimmune clearance or inhibition of VWF, increased shear-induced proteolysis of VWF, or increased binding of VWF to platelets or other cell surfaces. Autoimmune mechanisms may cause AVWS in association with lymphoproliferative diseases, monoclonal gammopathies, systemic lupus erythematosis, other autoimmune disorders, and some cancers. Autoantibodies to VWF have been detected in less than 20 percent of patients in whom they have been sought, suggesting that the methods for antibody detection may not be sufficiently sensitive or that AVWS in these settings may not always have an autoimmune basis.

Pathologic increases in fluid shear stress can occur with cardiovascular lesions, such as ventricular septal defect and aortic stenosis, or with primary pulmonary hypertension. The increased shear stress can increase the proteolysis of VWF by ADAMTS13 enough to deplete large VWF multimers and thereby produce a bleeding diathesis that resembles type 2A VWD. The VWF multimer distribution improves if the underlying cardiovascular condition is treated successfully.117-122

Increased binding to cell surfaces, particularly platelets, also can consume large VWF multimers. An inverse relationship exists between the platelet count and VWF multimer size, probably because increased encounters with platelets promote increased cleavage of VWF by ADAMTS13. This mechanism probably accounts for AVWS associated with myeloproliferative disorders; reduction of the platelet count can restore a normal VWF multimer distribution.123-125 In rare instances, VWF has been reported to bind GPIb that was expressed ectopically on tumor cells.118,126

AVWS has been described in hypothyroidism caused by nonimmune mechanism.127 Several drugs have been associated with AVWS; those most commonly reported include valproic acid, ciprofloxacin, griseofulvin, and hydroxyethyl starch.117,118

AVWS occurs in a variety of conditions, but other clinical features may direct attention away from this potential cause of bleeding. More studies are needed to determine the incidence of AVWS and to define its contribution to bleeding in the many diseases and conditions with which it is associated.

Prothrombotic Clinical Issues and VWF in Persons Who Do Not Have VWD

Whether elevation of VWF is prothrombotic has been the subject of several investigations. Both arterial and venous thrombotic disorders have been studied.

Open-heart surgery. Hemostatic activation after open-heart surgery has been suggested as a mechanism of increased risk of postoperative thrombosis in this setting. A randomized trial comparing coronary artery surgery with or without cardiopulmonary bypass ("off-pump") found a consistent and equivalent rise in VWF:Ag levels at 1-4 postoperative days in the two groups,128 suggesting that the surgery itself, rather than cardiopulmonary bypass, was responsible for the rise in VWF. There is no direct evidence that the postoperative rise in VWF contributes to the risk of thrombosis after cardiac surgery.

Coronary artery disease. Three large prospective studies of subjects without evidence of ischemic heart disease at entry have shown, by univariate analysis, a significant association of VWF:Ag level at entry with subsequent ischemic coronary events.129-131 However, the association remained significant by multivariate analysis in only one subset of subjects in these studies,129 a finding that could have occurred by chance. These findings suggest that the association of VWF with incidence of coronary ischemic events is relatively weak and may not be directly causal.

Thrombosis associated with atrial fibrillation. A prospective study of vascular events in subjects with atrial fibrillation found, by univariate analysis, a significant association of VWF:Ag level with subsequent stroke or vascular events. The association with vascular events remained significant with multivariate analysis.132

Thrombotic thrombocytopenic purpura (TTP). The hereditary deficiency or acquired inhibition of a VWF-cleaving protease, ADAMTS13, is associated with the survival in plasma of ultralarge VWF multimers, which are involved in the propensity to development of platelet-rich thrombi in the microvasculature of individuals who have TTP.133,134

Deep vein thrombosis (DVT). In a case-control study of 301 patients, evaluated at least 3 months after cessation of anticoagulation treatment for a first episode of DVT, plasma levels of VWF:Ag and FVIII activity were related to risk of DVT, according to univariate analysis. In multivariate analysis, the relation of VWF level with risk of DVT was not significant after adjustment for FVIII levels.135

Introduction

The evaluation of a person for possible VWD or other bleeding disorders may be initiated because of a variety of clinical indications (see Figure 3). These indications and situations may include evaluation of: (1) an asymptomatic person who will undergo a surgical or interventional procedure; (2) persons who present with current symptoms of or a history of increased bleeding, abnormal laboratory studies, and/or a positive family history of a bleeding disorder; or (3) persons who present with a prior diagnosis of VWD but do not have supporting laboratory documentation. In all cases, the initial step in assessment should focus on key aspects of the person’s clinical history to determine whether the person may benefit from further diagnostic evaluation. This section is divided into two parts. The first part uses a summary of the medical literature to provide suggested questions for an initial assessment of persons presenting for concerns about bleeding issues or for evaluation prior to procedures that may increase their risk of bleeding. Using the answers to the initial assessment, the second part focuses on a strategy for optimal laboratory assessment of those persons who potentially have bleeding disorders and suggests guidelines for interpretation of laboratory results.

Evaluation of the Patient

History, Signs, and Symptoms

The initial clinical assessment of a person who is being evaluated for VWD should focus on a personal history of excessive bleeding throughout the person’s life and any family history of a bleeding disorder. The history of bleeding should identify the spontaneity and severity, sites of bleeding, duration of bleeding, type of insult or injury associated with bleeding, ease with which bleeding can be stopped, and concurrent medications—such as aspirin, other nonsteroidal antiinflammatory drugs (NSAIDs), clopidogrel (Plavix?), warfarin, or heparin—at the onset of bleeding. Particularly when an invasive procedure is anticipated, the person should be asked whether he or she is currently taking any of these medications and also whether he or she has any history of liver or kidney disease, blood or bone marrow disease, or high or low platelet counts. If a history of any of these illnesses is present, further appropriate evaluation or referral should be undertaken.

Clinical manifestations. The most common presenting symptoms in persons subsequently diagnosed with VWD are summarized in Table 7. Symptoms usually involve mucous membranes and skin sites, and bleeding is of mild to moderate severity (bleeding that does not require blood transfusions and usually does not require visits to the physician) for most persons who have VWD, reflecting the predominance of type 1 VWD. However, life—threatening bleeding (CNS, gastrointestinal) can occur in persons who have type 3 VWD, in some persons who have type 2 VWD, and rarely in persons who have type 1 VWD. Uncommon bleeding manifestations, such as hemarthrosis, are more common in persons who have a more severe deficiency, especially those who have type 3 VWD.85,136 Clinical symptoms may also be modified by coexisting illnesses or other medications. For example, use of aspirin or other NSAIDs can exacerbate the bleeding tendency, whereas use of oral contraceptives can decrease bleeding in women who have VWD.

The clinical evaluation of bleeding symptoms is a challenge, because mild bleeding symptoms are also very common in healthy populations (Table 7, shaded column). Responses to questionnaires used to survey healthy controls indicate that they identify themselves as having specific bleeding manifestations as frequently as persons who have VWD, particularly type 1 VWD (Table 7).137,138,140,143 In addition, a family history of bleeding was reported by 44 percent of healthy children undergoing tonsillectomy143 and by 35 percent138 or 60 percent144 of persons referred because of bleeding. Because bleeding symptoms are so prevalent, it may be impossible to establish a causal relationship between bleeding and low VWF.

Figure 3. Initial Evaluation For VWD or Other Bleeding Disorders

Initial evaluation strategy to determine which patients would most benefit from further diagnostic evaluation for von Willebrand disease (VWD) Left Upper Box: Individuals would be asked three questions about their personal or family bleeding history which, if any are positive, would lead to a second set of questions selected for their sensitivity and specificity for VWD (Box 1, below). Those patients answering positively to one or more of the second set of questions would benefit from laboratory evaluation. Right Boxes: Patients presenting with specific information or a concern about bleeding would be asked the Box 1 questions and the initial 3 questions if not already asked, and would also undergo laboratory evaluation.

Some of the most important clinical issues in VWD apply specifically to women, particularly menorrhagia. Studies of women who have VWD report a high prevalence of menorrhagia (Table 7), although the definition of menorrhagia is not clearly specified in most of these studies and the diagnostic criteria for VWD are not uniform. The sensitivity of menorrhagia as a predictor of VWD may be estimated as 32-100 percent. However, menorrhagia is a common symptom, occurring with a similar frequency in healthy controls and women who have VWD; therefore, it is not a specific marker for VWD (Table 7). In a survey of 102 women who had VWD and were registered at hemophilia treatment centers in the United States, 95 percent reported a history of menorrhagia, but 61 percent of controls also reported a history of menorrhagia.145 Studies have reported a prevalence of VWD of between 5-20 percent among women who have menorrhagia.146-152 Therefore, the specificity of menorrhagia as a predictor of VWD can be estimated as 5-20 percent. Three findings that predict abnormal menstrual blood loss of >80 mL include:

• Clots greater than approximately 1 inch in diameter
• Low serum ferritin
• Changing a pad or tampon more than hourly153

Box 1. Suggested Questions for Screening Persons for a Bleeding Disorder

1. Do you have a blood relative who has a bleeding disorder, such as von Willebrand disease or hemophilia?
2. Have you ever had prolonged bleeding from trivial wounds, lasting more than 15 minutes or recurring spontaneously during the 7 days after the wound?
3. Have you ever had heavy, prolonged, or recurrent bleeding after surgical procedures, such as tonsillectomy?
4. Have you ever had bruising, with minimal or no apparent trauma, especially if you could feel a lump under the bruise?
5. Have you ever had a spontaneous nosebleed that required more than 10 minutes to stop or needed medical attention?
6. Have you ever had heavy, prolonged, or recurrent bleeding after dental extractions that required medical attention?
7. Have you ever had blood in your stool, unexplained by a specific anatomic lesion (such as an ulcer in the stomach, or a polyp in the colon), that required medical attention?
8. Have you ever had anemia requiring treatment or received blood transfusion?
9. For women, have you ever had heavy menses, characterized by the presence of clots greater than an inch in diameter and/or changing a pad or tampon more than hourly, or resulting in anemia or low iron level?

Sources: Dean JA, Blanchette VS, Carcao MD, Stain AM, Sparling CR, Siekmann J, Turecek PL, Lillicrap D, Rand ML. von Willebrand disease in a pediatric—based population—comparison of type 1 diagnostic criteria and use of the PFA—100® and a von Willebrand factor/collagenbinding assay. Thromb Haemost 2000 Sep;(3):401-409; Drews CD, Dilley AB, Lally C, Beckman MG, Evatt B. Screening questions to identify women with von Willebrand disease. J Am Med Womens Assoc 2002;57(4):217-218; and Laffan M, Brown SA, Collins PW, Cumming AM, Hill FG, Keeling D, Peake IR, Pasi KJ. The diagnosis of von Willebrand disease: a guideline from the UK Haemophilia Centre Doctors’ Organization. Haemophilia 2004 May;10(3):199-217.

Table 7. Common Bleeding Symptoms of Healthy Individuals and Patients Who Have VWD

* Calculated for females above 13 to 15 years of age. 
?341 individuals were sent a questionnaire, but the precise number of patients responding was not provided. 
?? Study included women only. 
? Study included males only. 
N.R., Not reported.

Identification of people who may require further evaluation for inherited bleeding disorders. Since other "bleeding symptoms" besides menorrhagia are reported frequently by persons who have apparently normal hemostasis, it is important to use questions that can best identify persons who have a true bleeding disorder. Sramek and colleagues138 used a written questionnaire with patients who had a proven bleeding disorder. When the responses were compared to those of a group of healthy volunteers, the most informative questions were related to: (1) prolonged bleeding after surgery, including after dental extractions, and (2) identification of family members who have an established bleeding disorder (Table 8, columns 2-5). A history of muscle or joint bleeding may also be helpful when associated with the above symptoms.

General questions that relate to isolated bleeding symptoms—such as frequent gingival bleeding, profuse menstrual blood loss, bleeding after delivery, and epistaxis in the absence of other bleeding symptoms—were not informative.138 The study also found that an elaborate interview after referral to a hematologist was not particularly helpful when attempting to distinguish persons who have a true bleeding disorder from persons who have a "suspected" bleeding disorder, implying that the selection of those with bleeding disorders had already been made by the referring physician.138

Drews et al.139 attempted to develop a questionnairebased screening tool to identify women who might benefit from a diagnostic workup for VWD. They conducted a telephone survey of 102 women who had a diagnosis of type 1 VWD and were treated at a hemophilia treatment center compared with 88 friends who were controls. With the exception of postpartum transfusions, all study variables were reported more frequently by women who had VWD than by their friends (Table 8, columns 6 and 7). In addition, positive responses to multiple questions were more likely to be obtained from patients who have an inherited bleeding disorder.139 An important limitation of this study is that these women were more symptomatic than most women diagnosed as having type 1 VWD, indicating a more severe phenotype of the disease; this fact might decrease the sensitivity of the questions in the setting of persons who have milder type 1 VWD and fewer symptoms.

More recently, Rodeghiero and colleagues155 compared responses to a standardized questionnaire obtained from 42 obligatory carriers of VWD (from well—characterized families) to responses from 215 controls. The questionnaire covered 10 common bleeding symptoms (including all symptoms in Table 7, and postpartum hemorrhage), with assigned scores for each ranging from 0 (no symptoms) to 3 (severe symptoms, usually including hospitalization and/or transfusion support). With this instrument, the researchers found that having a cumulative total bleeding score of 3 in men, or 5 in women, was very specific (98.6 percent) but not as sensitive (69.1 percent) for type 1 VWD. Limitations of this study include that it was retrospective and that the person administering the questionnaire was aware of the respondent’s diagnosis. This questionnaire is available online.155

A similar retrospective case-control study154 used a standardized questionnaire like that of Rodegherio et al.155 to assess bleeding symptoms of 144 index cases who had type 1 VWD, compared to 273 affected relatives, 295 unaffected relatives, and 195 healthy controls. The interviewers were not blinded to subject’s status. At least one bleeding symptom was reported by approximately 98 percent of index cases, 89 percent of affected relatives, 32 percent of unaffected relatives, and 12 percent of healthy controls. The major symptoms of affected persons (excluding index cases) included bleeding after tooth extraction, nosebleeds, menorrhagia, bleeding into the skin, postoperative bleeding, and bleeding from minor wounds. Using a bleeding score calculated from the data for comparison, the severity of bleeding diminished with increasing plasma VWF, not only for subjects who had low VWF levels but throughout the normal range as well. Although the mean bleeding score was significantly different between several groups, the distribution was sufficiently broad that the bleeding score could not predict the affected or unaffected status of individuals.

Table 8. Prevalences of Characteristics in Patients Who Have Diagnosed Bleeding Disorders Versus Healthy Controls

Sources: Sramek A, Eikenboom JC, Briet E, Vandenbroucke JP, Rosendaal FR. Usefulness of patient interview in bleeding disorders. Arch Intern Med 1995 Jul;155(13):1409-1415; Drews CD, Dilley AB, Lally C, Beckman MG, Evatt B. Screening questions to identify women with von Willebrand disease. J Am Med Womens Assoc 2002;57(4):217-218; and Tosetto A, Rodeghiero F, Castaman G, Goodeve A, Federici AB, Batlle J, Meyer D, Fressinaud E, Mazurier C, Goudemand J, et al. A quantitative analysis of bleeding symptoms in type 1 von Willebrand disease: results from a multicenter European study (MCMDM—1 VWD). J Thrombos Haemostas 2006;4:766-773. 
* Univariate and multivariate analyses from reference comparing 222 patients who had a known bleeding disorder (43 percent mild VWD) to 341 healthy volunteers.138
? Compiled from responses to a questionnaire sent to 102 women, who had type 1 VWD, in a hemophilia treatment center.139
? Compiled from interviews comparing affected vs. unaffected family members of patients who have type 1 VWD. The index cases (patients who have VWD) were not included in the analysis (Tosetto et al. 2006, and personal communication from Dr. Francesco Rodeghiero on behalf of coauthors).154
CI, confidence interval

In a related study, bleeding symptoms were assessed with the same questionnaire in 70 persons who were obligatory carriers of type 3 VWD, 42 persons who were obligate carriers of type 1 VWD (meaning affected family members of index cases who had type 1 VWD), and 215 persons who were healthy controls.156 Carriers of type 3 VWD were compared with carriers of type 1 VWD to address the question of whether the distinct types of VWF mutations associated with these conditions predisposed to the same or different severity of bleeding. Approximately 40 percent of carriers of type 3 VWD, 82 percent of carriers of type 1 VWD, and 23 percent of healthy controls had at least one bleeding symptom. The major bleeding symptoms in carriers of type 3 VWD were bleeding into skin and postsurgical bleeding. The results suggest that carriers of type 3 VWD are somewhat distinct, as they have bleeding symptoms more frequently than healthy controls but less frequently than persons who have or are carriers of type 1 VWD. Usually, carriers of type 1 VWD have lower VWF levels than carriers of type 3 VWD.

Family history. Although a family history that is positive for an established bleeding disorder is useful in identifying persons who are likely to have VWD, such a history is frequently not present. This is most commonly the case for persons who have milder forms of VWD and whose family members may have minimal, if any, symptoms. As shown in Table 8, the presence of a documented bleeding disorder in a family member is extremely helpful in deciding which persons to evaluate further, whereas a family history of bleeding symptoms is less helpful.

Box 1 summarizes suggested questions that can be used to identify persons who should be considered for further evaluation for VWD with laboratory studies.

Physical examination. The physical examination should be directed to confirm evidence for a bleeding disorder, including size, location, and distribution of ecchymoses (e.g., truncal), hematomas, petechiae, and other evidence of recent bleeding. The examination should also focus on findings that may suggest other causes of increased bleeding, such as evidence of liver disease (e.g., jaundice), splenomegaly, arthropathy, joint and skin laxity (e.g., Ehlers—Danlos Syndrome), telangiectasia (e.g., hereditary hemorraghic telangiectasia), signs of anemia, or anatomic lesions on gynecologic examination.

Acquired von Willebrand Syndrome (AVWS). Persons who have AVWS present with bleeding symptoms similar to those described, except that the past personal and family history are negative for bleeding symptoms. AVWS may occur spontaneously or in association with other diseases, such as monoclonal gammopathies, other plasma cell dyscrasias, lymphoproliferative diseases, myeloproliferative disorders (e.g., essential thrombocythemia), autoimmune disorders, valvular and congenital heart disease, certain tumors, and hypothyroidism.117,157 The evaluation should be tailored to finding conditions associated with AVWS.

Laboratory Diagnosis and Monitoring

An algorithm for using clinical laboratory studies to make the diagnosis of VWD is summarized in Figure 4.

Ideally, a simple, single laboratory test could screen for the presence of VWD. Such a screening test would need to be sensitive to the presence of most types of VWD and would have a low false—positive rate. Unfortunately, no such test is available. In the past, the activated partial thromboplastin time (PTT) and bleeding time (BT) were recommended as diagnostic tests. These tests were probably satisfactory for detecting severe type 3 VWD, but as variant VWD and milder forms of VWD were characterized, it became apparent that many of the persons who have these conditions had normal PTT and normal BT results.

An initial hemostasis laboratory evaluation (see Box 2) usually includes a platelet count and complete blood count (CBC), PTT, prothrombin time (PT), and optionally either a fibrinogen level or a thrombin time (TT). This testing neither "rules in" nor "rules out" VWD, but it can suggest whether coagulation factor deficiency or thrombocytopenia might be the potential cause of clinical bleeding. If the mucocutaneous bleeding history is strong, consider performing initial VWD assays (VWF:Ag, VWF:RCo, and FVIII) at the first visit.

Box 2. Initial Laboratory Evaluation of Hemostasis

• CBC and platelet count
• PTT
• PT
• Fibrinogen or TT (optional)

Figure 4. Laboratory Assessment For VWD or Other Bleeding Disorders

* Isolated decreased platelets may occur in VWD type 2B. 
? Correction in the PTT mixing study immediately and after 2—hour incubation removes a factor VIII (FVIII) inhibitor from consideration. 
Investigation of other intrinsic factors and lupus anticoagulant also may be indicated. 
CBC, complete blood count; PT prothrombin time; PTT partial thromboplastin time; RIPA, ristocetin—induced platelet aggregation; TT, thrombin time; VWF:Ag, VWF antigen; VWF:RCo, VWF ristocetin cofactor activity.

If the initial clinical evaluation suggests a bleeding disorder, the "initial hemostasis tests" should be ordered, followed by or along with the next tests ("initial VWD assays") indicated in the algorithm. Referral to a hemostasis specialist is appropriate for help in interpretation, repeat testing, and specialized tests.

Some centers add a BT or a platelet function analyzer (PFA—100®) assay to their initial laboratory tests. The BT test is a nonspecific test and is fraught with operational variation. It has been argued that it was a population—based test that was never developed to test individuals.158 Variables that may affect results include a crying or wiggling child, differences in the application of the blood pressure cuff, and the location, direction, and depth of the cut made by the device.

This test also has a potential for causing keloid formation and scarring, particularly in non—Caucasian individuals. The PFA—100® result has been demonstrated to be abnormal in the majority of persons who have VWD, other than those who have type 2N, but its use for population screening for VWD has not been established.159-162 Persons who have severe type 1 VWD or who have type 3 VWD usually have abnormal PFA—100® values, whereas persons who have mild or moderate type 1 VWD and some who have type 2 VWD may not have abnormal results.163-165 When persons are studied by using both the BT and PFA—100®, the results are not always concordant.162,164,166

When using the PTT in the diagnosis of VWD, results of this test are abnormal only if the FVIII is sufficiently reduced. Because the FVIII gene is normal in VWD, the FVIII deficiency is secondary to the deficiency of VWF, its carrier protein. In normal individuals, the levels of FVIII and VWF:RCo are approximately equal, with both averaging 100 IU/dL. In type 3 VWD, the plasma FVIII level is usually less than 10 IU/dL and represents the steady state of FVIII in the absence of its carrier protein. In persons who have type 1 VWD, the FVIII level is often slightly higher than the VWF level and may fall within the normal range. In persons who have type 2 VWD (except for type 2N VWD in which it is decreased), the FVIII is often 2-3 times higher than the VWF activity (VWF:RCo).167,168 Therefore, the PTT is often within the normal range. If VWF clearance is the cause of low VWF, the FVIII reduction parallels that of VWF, probably because both proteins are cleared together as a complex.

Initial Tests for VWD

Box 3 lists the initial tests commonly used to detect VWD or low VWF. These three tests, readily available in most larger hospitals, measure the amount of VWF protein present in plasma (VWF:Ag), the function of the VWF protein that is present as ristocetin cofactor activity (VWF:RCo), and the ability of the VWF to serve as the carrier protein to maintain normal FVIII survival, respectively. If any of the above tests is abnormally low, the next steps should be discussed with a coagulation specialist, who may recommend referral to a specialized center, and/or repeating the laboratory tests plus performing additional tests.

VWF:Ag is an immunoassay that measures the concentration of VWF protein in plasma. Commonly used methods are based on enzyme—linked immunosorbent assay (ELISA) or automated latex immunoassay (LIA). As discussed below, the standard reference plasma is critical and should be referenced to the World Health Organization (WHO) standard. The person’s test results should be reported in international units (IU), either as international units per deciliter (IU/dL) or as international units per milliliter (IU/mL). Most laboratories choose IU/dL, because it is similar to the conventional manner of reporting clotting factor assays as a percentage of normal.

VWF:RCo is a functional assay of VWF that measures its ability to interact with normal platelets. The antibiotic, ristocetin, causes VWF to bind to platelets, resulting in platelet clumps and their removal from the circulation. Ristocetin was removed from clinical trials because it caused thrombocytopenia. This interaction was developed into a laboratory test that is still the most widely accepted functional test for VWF. (In vivo, however, it is the high shear in the microcirculation, and not a ristocetin—like molecule, that causes the structural changes in VWF that lead to VWF binding to platelets.)

Box 3. Initial Tests for VWD

• VWF:Ag
• VWF:RCo
• FVIII

Several methods are used to assess the platelet agglutination and aggregation that result from the binding of VWF to platelet GPIb induced by ristocetin (ristocetin cofactor activity, or VWF:RCo). The methods include: (1) time to visible platelet clumping using ristocetin, washed normal platelets (fresh or formalinized), and dilutions of patient plasma; (2) slope of aggregation during platelet aggregometry using ristocetin, washed normal platelets, and dilutions of the person’s plasma; (3) automated turbidometric tests that detect platelet clumping, using the same reagents noted above; (4) ELISA assays that assess direct binding of the person’s plasma VWF to platelet GPIb (the GPIb may be derived from plasma glycocalicin) in the presence of ristocetin;169-171 and (5) the binding of a monoclonal antibody to a conformation epitope of the VWF A1 loop.172 Method 5 can be performed in an ELISA format or in an automated latex immunoassay. It is not based on ristocetin binding. The first three assays (above) may use platelet membrane fragments containing GPIb rather than whole platelets. The sensitivity varies for each laboratory and each assay; in general, however, Methods 1 and 2, which measure platelet clumping by using several dilutions of the person’s plasma, are quantitative to approximately 6-12 IU/dL levels. Method 3 is quantitative to about 10-20 IU/dL. Method 4 can measure VWF:RCo to <1 IU/dL, and a variation of it can detect the increased VWF binding to GPIb seen in type 2B VWD.173 Some automated methods are less sensitive and require modification of the assay to detect <10 IU/dL. Each laboratory should define the linearity and limits of its assay. Several monoclonal ELISAs (Method 5) that use antibodies directed to the VWF epitope containing the GPIb binding site have been debated because the increased function of the largest VWF multimers is not directly assessed.174

The ristocetin cofactor activity (VWF:RCo) assay has high intra- and interlaboratory variation, and it does not actually measure physiologic function. The coefficient of variation (CV) has been measured in laboratory surveys at 30 percent or greater, and the CV is still higher when the VWF:RCo is lower than 12-15 IU/dL.175-179 This becomes important not only for the initial diagnosis of VWD, but also for determining whether the patient has type 1 versus type 2 VWD (see discussion on VWF:RCo to VWF:Ag ratio, below). Despite these limitations, it is still the most widely accepted laboratory measure of VWF function. Results for VWF:RCo should be expressed in international units per deciliter (IU/dL) based on the WHO plasma standard.

FVIII coagulant assay is a measure of the cofactor function of the clotting factor, FVIII, in plasma. In the context of VWD, FVIII activity measures the ability of VWF to bind and maintain the level of FVIII in the circulation. In the United States, the assay is usually performed as a one—stage clotting assay based on the PTT, although some laboratories use a chromogenic assay. The clotting assay, commonly done using an automated or semiautomated instrument, measures the ability of plasma FVIII to shorten the clotting time of FVIII—deficient plasma. Because this test is important in the diagnosis of hemophilia, the efforts to standardize this assay have been greater than for other hemostasis assays. FVIII activity is labile, with the potential for spuriously low assay results if blood specimen collection, transport, or processing is suboptimal. Like those tests discussed above, it should be expressed in international units per deciliter (IU/dL) based on the WHO plasma standard.

Expected patterns of laboratory results in different subtypes of VWD, depicted in Figure 5, include results of the three initial VWD tests (VWF:Ag, VWF:RCo, FVIII) and results of other assays for defining and classifying VWD subtypes. The three initial tests (or at least the VWF:RCo and FVIII assays) are also used for monitoring therapy.

Other Assays To Measure VWF, Define/Diagnose VWD, and Classify Subtypes

The VWF multimer test, an assay that is available in some larger centers and in commercial laboratories, is usually performed after the initial VWD testing indicates an abnormality, preferably using a previously unthawed portion of the same sample or in association with a repeated VWD test panel (VWF:Ag, VWF:RCo, FVIII) using a fresh plasma sample. VWF multimer analysis is a qualitative assay that depicts the variable concentrations of the different—sized VWF multimers by using sodium dodecyl sulfate (SDS)—protein electrophoresis followed by detection of the VWF multimers in the gel, using a radiolabeled polyclonal antibody or a combination of monoclonal antibodies. Alternatively, the protein is transferred to a membrane (Western blot), and the multimers are identified by immunofluorescence or other staining techniques.99,180,181

Figure 5. Expected Laboratory Values in VWD

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The symbols and values represent prototypical cases. In practice, laboratory studies in certain patients may deviate slightly from these expectations.

L, 30—50 IU/dL; ?, ??, ???, relative decrease; ?, ??, ???, relative increase; BT, bleeding time; FVIII, factor VIII activity; LD—RIPA, low—dose ristocetin—induced platelet aggregation (concentration of ristocetin ? 0.6 mg/mL); N, normal; PFA—100® CT, platelet function analyzer closure time; RIPA, ristocetin—induced platelet aggregation; VWF, von Willebrand factor; VWF:Ag, VWF antigen; VWF:RCo, VWF ristocetin cofactor activity.

*Note: persons who have platelet—type VWD (PLT—VWD) have a defect in their platelet GPIb. Laboratory test results resemble type 2B VWD, and both have a defect in their LD—RIPA. In the VWF:platelet binding assay (see text), persons who have type 2B VWD have abnormally increased platelet binding. Normal persons and those who have PLT—VWD have no binding of their VWF to normal platelets at low ristocetin concentrations.

Note: this figure is adapted from and used by permission of R.R. Montgomery.

Multimer assays are designated as "low resolution" (which differentiate the largest multimers from the intermediate and small multimers) or "high resolution" (which differentiate each multimer band of the smaller multimers into three to eight satellite bands). For diagnostic purposes, the low—resolution gel systems are used primarily; these systems help to differentiate the type 2 VWD variants from types 1 or 3 VWD. Figure 6 illustrates the differences between these two techniques with regard to the resolution of high— and low—molecular—weight multimers. It should be noted that multimer appearance alone does not define the variant subtype and that only types 2A, 2B, and platelet—type VWD (PLT—VWD) have abnormal multimer distributions with relative deficiency of the largest multimers. An exception is Vicenza variant VWD with ultralarge VWF multimers and low VWF. For more information about VWF multimer findings in type 2 VWD variants, see descriptions above (type 2 VWD) and associated references.

Low—Dose RIPA. RIPA and VWF platelet—binding assay (VWF:PB assay) are two tests that are performed to aid in diagnosing type 2B VWD. RIPA may be done as part of routine platelet aggregation testing. RIPA is carried out in platelet—rich plasma, using a low concentration of ristocetin (usually <0.6 mg/mL, although ristocetin lots vary, resulting in the use of slightly different ristocetin concentrations). This low concentration of ristocetin does not cause VWF binding and aggregation of platelets in samples from normal persons, but it does cause VWF binding and aggregation of platelets in samples from patients who have either type 2B VWD or mutations in the platelet VWF receptor. The latter defects have been termed platelet—type (PLT—VWD) or pseudo VWD, and they can be differentiated from type 2B VWD by VWF:PB assay. At higher concentrations of ristocetin (1.1-1.3 mg/mL), RIPA will be reduced in persons who have type 3 VWD. However, the test is not sufficiently sensitive to reliably diagnose other types of VWD.

Figure 6. Analysis of VWF Multimers

The distribution of VWF multimers can be analyzed using sodium dodecyl sulfate (SDS)—agarose electrophoresis followed by immunostaining. Low—resolution gels (0.65% agarose, left side) can demonstrate the change in multimer distribution of the larger multimers (top of the gel), while high—resolution gels (2-3% agarose, right side) can separate each multimer into several bands that may be distinctive. For example, the lowest band in the 0.65% gel (1) can be resolved into 5 bands in the 3% agarose gel, but the 3% gel fails to demonstrate the loss of high molecular weight multimers seen at the top in the 0.65% gel. The dotted lines (1) indicate the resolution of the smallest band into several bands in the 3% agarose gel. In each gel, normal plasma (NP) is run as a control. Type 1 VWD plasma has all sizes of multimers, but they are reduced in concentration. Type 2A VWD plasma is missing the largest and intermediate multimers, while type 2B VWD plasma is usually missing just the largest VWF multimers. No multimers are identified in type 3 VWD plasma. Patients who have thrombotic thrombocytopenic purpura (TTP) may have larger than normal multimers when studied with low—resolution gels. 
Note: Used by permission of R.R. Montgomery.

VWF: platelet—binding (VWF:PB) assay measures the binding of VWF to normal paraformaldehyde—fixed platelets using low concentrations of ristocetin (usually 0.3-0.6 mg/mL).182 The amount of VWF bound to the fixed platelets is determined by using a labeled antibody. Normal individuals, or those who have types 1, 2A, 2M, 2N, and 3 VWD, exhibit minimal or no binding to platelets at the concentration of ristocetin used, but patients who have type 2B VWD exhibit significant binding that causes their variant phenotype (a loss of high—molecular—weight multimers, decreased ristocetin cofactor activity, and thrombocytopenia). Both type 2B VWD and platelet—type VWD have agglutination of platelet—rich plasma (PRP) to low—dose ristocetin, but the VWF:PB assay can differentiate type 2B VWD from platelettype VWD. Only VWF from persons who have type 2B VWD has increased VWF:PB, while VWF from persons who have platelet—type VWD has normal VWF:PB with low doses of ristocetin.

VWF collagen—binding (VWF:CB) assay measures binding of VWF to collagen. The primary site of fibrillar collagen binding is in the A3 domain of VWF. Like the ristocetin cofactor assay, the collagen binding assay is dependent on VWF multimeric size, with the largest multimers binding more avidly than the smaller forms. The VWF:CB assay performance and sensitivity to VWD detection or discrimination among VWD subtypes is highly dependent on the source of collagen, as well as on whether type 1 collagen or a mixture of type 1/3 collagen is used.183,184 Only a few patients have been identified who have specific collagen—binding defects that are independent of multimer size, and the defects have been associated with a mutation of VWF in the A3 domain.73 The prevalence of such defects is unknown. The place of VWF:CB in the evaluation of VWD has not been established. In principle, however, patients who have defects in collagen binding may have a normal VWF:RCo and thus escape clinical diagnosis unless a VWF:CB assay is performed. Limited studies suggest that supplementary VWF:CB testing, complementing assays of VWF:RCo and VWF:Ag, can improve the differentiation of type 1 VWD from types 2A, 2B, or 2M VWD.175,185,186

VWF:FVIII binding (VWF:FVIIIB) assay measures the ability of a person’s VWF to bind added exogenous FVIII and is used to diagnose type 2N VWD.75,77,78,187,188 The assay is performed by capturing the person’s VWF on an ELISA plate, removing the bound endogenous FVIII, and then adding back a defined concentration of exogenous recombinant FVIII. The amount of FVIII bound is determined by a chromogenic FVIII assay. The level of this bound FVIII is then related to the amount of the person’s VWF initially bound in the same well. In clinical experience, Type 2N VWD is usually recessive; the person is either homozygous or compound heterozygous (one allele is type 2N, and the other is a type 1 or "null" allele). In either case, the VWF in the circulation does not bind FVIII normally, and the concentration of FVIII is thus decreased.

The VWF:RCo to VWF:Ag ratio can aid in the diagnosis of types 2A, 2B, and 2M VWD and help differentiate them from type 1 VWD. For example, VWF:RCo/VWF:Ag <0.6189 or <0.7 has been used as a criterion for dysfunctional VWF.8,190 A similar approach has been proposed for the use of the VWF:CB/VWF:Ag ratio.8,190 In type 2A VWD, the ratio is usually low; and in type 2B VWD, the VWF:RCo/VWF:Ag ratio is usually low but may be normal. In type 2M VWD, the VWF:Ag concentration may be reduced or normal, but the VWF:RCo/VWF:Ag ratio will be <0.7. One study70 determined the VWF:RCo/VWF:Ag ratio in nearly 600 individuals with VWF levels <55 IU/dL who had normal VWF multimers. The study used this ratio to identify families who had type 2 VWD, but most centers do not have the ability to establish normal ranges for patients who have low VWF. Additionally, the VWF:RCo assay has a coefficient of variation (CV) as high as 30 percent or more, depending on methodology, whereas the CV for the VWF:Ag assay is somewhat lower. The high intrinsic variability of the VWF:RCo assay, especially at low levels of VWF, can make the VWF:RCo/VWF:Ag ratio an unreliable criterion for the diagnosis of type 2 VWD.175,177-179 (See Recommendations II.C.1.a. and III.B.1, below). It is important that the same plasma standard be used in both the VWF:RCo and VWF:Ag assays and that the normal range for the VWF:RCo/VWF:Ag ratio and its sensitivity to types 2A and 2M VWD be determined in each laboratory. Because no large multicenter studies have evaluated the precise ratio that should be considered abnormal, a ratio in the range of less than 0.5-0.7 should raise the suspicion of types 2A, 2B, or 2M VWD. Further confirmation should be sought by additional testing (e.g., repeat VWD test panel and VWF multimer study or sequencing of the A1 region of the VWF gene).191

ABO blood types have a significant effect on plasma VWF (and FVIII) concentrations.43,192 Individuals who have blood type O have concentrations approximately 25 percent lower compared to persons who have other ABO blood types. The diagnosis of type 1 VWD occurs more frequently in individuals who have blood group type O.43Table 9 illustrates the significant effect of blood type on VWF:Ag level.

Table 9. Influence of ABO Blood Groups on VWF:Ag

*U/dL; ?IU/dL 
Source: Gill JC, Endres—Brooks J, Bauer PJ, Marks WJ, Jr., Montgomery RR. The effect of ABO blood group on the diagnosis of von Willebrand disease. Blood 1987 Jun;69(6):1691-1695. Copyright American Society of Hematology, used with permission. In this publication, VWF:Ag was expressed as U/dL, but the range in IU/dL (WHO) is higher for all blood groups, as noted in the values in parentheses (personal communication from R.R. Montgomery, J.L. Endres, and K.D. Friedman).

Although it has been recommended to stratify reference ranges for VWF:Ag and VWF:RCo with respect to blood group O and nongroup O,193,194 evolving limited information supports the concept that, despite the ABO blood grouping and associated VWF reference ranges, the major determinant of bleeding symptoms or risk is low VWF.189,195,196 Therefore, referencing VWF testing results to the population reference range, rather than to ABO—stratified reference ranges, may be more useful clinically.

Platelet VWF studies are performed by some laboratories, including VWF:RCo, VWF:Ag, and VWF multimers, using VWF extracted from washed platelets. The methods and interpretations of these studies, however, are not well standardized.

DNA sequencing of patient DNA has been used to make a molecular diagnosis of variants of type 2 VWD,197-199 but DNA sequencing is not widely available. Most of the mutations found in types 2B, 2M, and 2N VWD cluster in the cDNA that directs the synthesis of specific regions of VWF (see Figure 2).200 In the common forms of type 2A VWD, in which the VWF is spontaneously cleaved by ADAMTS13, mutations cluster in the A2 domain (which contains the cleavage site). In the less common type 2A variants of VWD, in which multimer formation is inhibited, the mutations may be scattered throughout the gene. In most persons who have type 1 VWD, the genetic mutations have not been established, although several studies are being conducted at present to characterize these mutations.

Assays for Detecting VWF Antibody

Assays for detecting anti—VWF antibodies are not as well established as the assays for detecting antibodies to FVIII in patients who have hemophilia A. Some patients who have AVWS do appear to have anti—VWF antibodies that decrease the half—life of infused VWF. Although a few antibodies do inhibit VWF function and can be demonstrated in 1:1 mixing studies with normal plasma using the VWF:RCo assay, most anti—VWF antibodies are not "inhibitors" of VWF function. The presence of these antibodies, however, promotes rapid clearance of VWF. The plasma level of VWF propeptide (VWFpp) is normally proportionate to the level of VWF:Ag, and the VWFpp level can be measured to aid in the detection of the rapid clearance of VWF. Accelerated plasma clearance of VWF:Ag—as occurs in some patients who have AVWS, in those who have certain type 1 VWD variants, or in those who have type 3 VWD and have alloantibodies to VWF—is associated with an increase in the ratio of VWFpp to VWF:Ag.201,202 Persons who have type 3 VWD, with large deletions of the VWF gene, are prone to develop alloantibodies to transfused VWF.203 Patients who have AVWS, VWF antibodies, or mutations that affect VWF clearance can be studied using VWF—survival testing after administration of DDAVP or VWF concentrate.

Making the Diagnosis of VWD

Scoring systems and criteria for assessing the bleeding history and the probability of having VWD, especially type 1 VWD, are in evolution but have not yet been subjected to prospective studies outside of defined populations.155,194 Establishing the diagnosis of VWD in persons who have type 2 VWD variants and type 3 VWD is usually straightforward, based on the initial VWD tests (described in Box 3 above, Initial Tests for VWD). Treatment depends on the specific subtype (e.g., type 2A, 2B, 2M, or 2N), which is determined by additional tests including VWF multimer analysis. In contrast, the diagnosis of type 1 VWD is often more difficult,21,44,93,114,204 partly because not all persons who have decreased levels of VWF have a molecular defect in the VWF gene. Whether individuals who do not have an abnormality in the VWF gene should be diagnosed as having VWD or should be given another designation is currently under consideration (see section on "Type 1 VWD Versus Low VWF"). The reasons for reduced VWF levels in many of these persons who have a normal VWF gene sequence are not understood. A "low" VWF level is believed to confer some bleeding risk, despite having a normal VWF gene, and those persons who have clinical bleeding and low VWF may benefit from treatment to raise the VWF level. Most clinicians would agree that persons having VWF levels below 30 IU/dL probably have VWD. It is likely that most of these persons have a mutation in the VWF gene. Currently, several large European Union, Canadian, and U.S. studies are trying to define that frequency. Persons whose plasma VWF levels are below the lower limit of the laboratory reference range, but >30 IU/dL, may have VWD but are sometimes referred to as having "possible type 1 VWD" or "low VWF." There is no generally accepted designation for these persons. Although type 3 VWD is usually the result of inheriting two "null" alleles, the heterozygous "carriers" in these families do not universally have a significant bleeding history; therefore, type 3 VWD has been called a recessive disorder.21,44,101

Special Considerations for Laboratory Diagnosis of VWD

Repeated testing for VWD is sometimes needed to identify low levels of VWF. Stress—including surgery, exercise, anxiety, crying in a frightened child, as well as systemic inflammation, pregnancy, or administration of estrogen/oral contraceptives— can cause an increase in plasma levels of VWF and mask lower baseline values. VWF levels vary with the menstrual cycle, and lowest values are detected on days 1-4 of the menstrual cycle. However, the importance of timing of the testing with respect to the menstrual cycle is not clear. Family studies may be helpful to diagnose hereditary decreases in VWF levels.

Problems may occur in preparing samples for testing. As noted, anxiety may falsely elevate the VWF and FVIII levels, and the setting for phlebotomy should be as calm as possible. It is important that the sample be obtained by atraumatic collection of blood, drawn into the appropriate amount of citrate anticoagulant. The College of American Pathologists (CAP), as well as the Clinical Laboratory Standards Institute (CLSI, formerly NCCLS), recommend collecting blood into 3.2 percent citrate, although some laboratories still use 3.8 percent citrate. Fasting or nonlipemic samples should be used for testing, and icteric or hemolyzed samples may also compromise the quality of testing results.193,205 If a person has polycythemia or profound anemia, the amount of anticoagulant should be adjusted on the basis of nomograms for this purpose. Blood should be centrifuged promptly to obtain plasma, and the plasma should remain at room temperature if assays are to be completed within 2 hours. Whole blood should not be transported on wet ice (or frozen).206,207 If plasma samples are frozen, they should be thawed at 37°C to avoid formation of a cryoprecipitate. Plasma assays should be performed on "platelet—poor" or "platelet—free" plasma.193 Although a small number of platelets may not significantly affect studies done on fresh plasma, freezing these samples may result in the release of proteases or platelet membrane particles that affect plasma assays for VWF. Thus, plasmas should be centrifuged carefully. Some laboratories perform double centrifugation to ensure platelet removal. The integrity of samples may suffer during transport to an outside laboratory, and steps should be taken that can best ensure prompt delivery of frozen samples. (See Table 10, below.)

The VWF reference standard is critical to the laboratory diagnosis of VWD. When possible, all laboratory assays of VWF should use the same standard to avoid artifactual discrepancies. Results of VWF assays can be reported in international units (IUs) only if they have been referenced to the WHO standard for that analyte. If a reference plasma pool is used, it is usually reported as a percentage of normal, as it cannot be called an IU. To assist the comparison, IUs are usually expressed as IU/dL so that the reported values have the same range as "percentage of normal plasma" values.

Table 10. Collection and Handling of Plasma Samples for Laboratory Testing

Phlebotomy conditions—An atraumatic blood draw limits the exposure of tissue factor from the site and the activation of clotting factors, minimizing falsely high or low values.

Patient stress level—Undue stress, such as struggling or crying in children or anxiety in adults, may falsely elevate VWF and FVIII levels. Very recent exercise can also elevate VWF levels.

Additional conditions in the person—The presence of an acute or chronic inflammatory illness may elevate VWF and FVIII levels, as may pregnancy or administration of estrogen/oral contraceptives.

Sample processing—To prevent cryoprecipitation of VWF and other proteins, blood samples for VWF assays should be transported to the laboratory at room temperature. Plasma should be separated from blood cells promptly at room temperature, and the plasma should be centrifuged thoroughly to remove platelets. If plasma samples will be assayed within 2 hours, they should be kept at room temperature. Frozen plasma samples should be carefully thawed at 37°C and kept at room temperature for <2 hours before assay.

Sample storage—Plasma samples that will be stored or transported to a reference laboratory must be frozen promptly at or below -40°C and remain frozen until assayed. A control sample that is drawn, processed, stored, and transported under the same conditions as the tested person’s sample may be helpful in indicating problems in the handling of important test samples.

Laboratory variables also occur. The variability (CV) of the VWF:RCo assay is high (20-30 percent or greater) and the CV of the VWF:Ag assay is also relatively high (10-20 percent or greater), as is the CV for the FVIII assay.175,177-179,183,208-210 The quality of laboratory testing also varies considerably among laboratories (high interlaboratory CV). Coupled with variability of VWF and FVIII contributed by conditions of the patient and the blood sample, the high variability of these three diagnostic tests can contribute to difficulty in diagnosing VWD or classifying the VWD subtype (e.g., type 1 vs. type 2 variant, using the VWF:RCo to VWF:Ag ratio). Some of the more specialized tests, such as VWF multimer analysis likely also have high variability of test performance and interpretation,180,181 and they are often not available at local testing laboratories.

Summary of the Laboratory Diagnosis of VWD

The diagnosis of VWD can be complex, and no single diagnostic approach is suitable for all patients. Improvements in laboratory testing and quality, along with further research into the frequency of mutations of the VWF gene, alterations of other proteins that result in reduced VWF levels, and the correlation of clinical symptoms with laboratory test levels will be necessary to place the diagnosis of VWD on a more secure foundation. (See Table 10, above.)

The following recommendations include specific clinical history, physical findings, laboratory assays, and diagnostic criteria that this Panel suggests will allow the most definitive diagnosis of VWD.

• Tests such as the bleeding time, PFA—100®, or other automated functional platelet assays have been used but there are conflicting data with regard to sensitivity and specificity for VWD.162,164,166 Therefore, the Panel believes current evidence does not support their routine use as screening tests for VWD.
• The Panel believes that platelet—based assays should be used for the ristocetin cofactor method.
• The Panel emphasizes the importance of the timing of the phlebotomy for assays, with the patient at his/her optimal baseline as far as possible. (For example, VWF levels may be elevated above baseline during the second and third trimesters of pregnancy or during estrogen replacement, during acute inflammation such as the perioperative period, during infections, and during acute stress.) The careful handling and processing of the sample is also critical, particularly if the sample will be sent out for testing at a distant location.

Diagnostic Recommendations

The recommendations are graded according to criteria described in "Clinical Recommendations—Grading and Levels of Evidence" and Table 1. Evidence tables are provided for recommendations given a grade of B and having two or more references.

1. Evaluation of Bleeding Symptoms and Bleeding Risk by History and Physical Examination Summarized in Figure 3, and Box 1.

• Ask the following broad questions:
  • Have you or a blood relative ever needed medical attention for a bleeding problem, or have you been told you had a bleeding problem? Grade B, level IIb138 
  • If the answer is "Yes" to either of the broad questions above, ask the additional probes:
    • Have you needed medical attention for bleeding? After surgery? After dental work? With trauma?
    • Have you ever had bruises so large they had lumps? Grade B, level IIb138
  • Do you have or have you ever had:
    • Liver or kidney disease?
    • A blood or bone marrow disorder?
    • A high or low platelet count? 
    • If the answer is "Yes" to any of these questions, obtain relevant details. Grade C, level IV
  • Are you currently taking, or have you recently taken anticoagulation or antiplatelet medications (warfarin, heparin, aspirin, NSAIDs, clopidogrel)? 
  • If the answer is "Yes", obtain relevant details. Grade C, level IV
• If answers to questions I.A.1 are positive, ask if the patient or any blood relatives have had:
  • A bleeding disorder, such as von Willebrand disease or hemophilia?
  • Prolonged bleeding, heavy, or recurrent from:
    • Trivial wounds, lasting more than 15 minutes or recurring spontaneously during the 7 days after the wound?
    • Surgical procedures, such as tonsillectomy?
  • Bruising with minimal or no apparent trauma, especially if you could feel a lump?
  • Spontaneous nosebleeds that required more than 10 minutes to stop or needed medical attention?
  • Dental extractions leading to heavy, prolonged, or recurrent bleeding?
  • Blood in your stool, unexplained by a specific anatomic lesion (such as an ulcer in the stomach, or a polyp in the colon), that required medical attention?
  • Anemia requiring treatment or received a blood transfusion?
  • For women, heavy menses, characterized by the presence of clots greater than an inch in size and/or changing a pad or tampon more than hourly, or resulting in anemia or low iron level? 
  • If answers to above questions I.B.1-8 are positive, obtain relevant specific information. Grade B, level IIb138,139See Evidence Table 1.
• Perform a physical examination to include evaluation for:
  • Evidence for a bleeding disorder, including size, location, and distribution of ecchymoses (e.g., truncal), hematomas, petechiae, and other evidence of recent bleeding and/or anemia. Grade C, level IV
  • Evidence that suggests other causes or risks of increased bleeding, such as jaundice or spider angiomata (liver disease), splenomegaly, arthropathy, joint and skin laxity (e.g., Ehlers—Danlos Syndrome), telangiectasia (e.g., hereditary hemorraghic telangiectasia), or evidence of anatomic lesions on gynecologic examination. Grade C, level IV

Laboratory testing should be guided by the history and physical findings (section I.) and the initial laboratory evaluation (see II.A., below). For example, findings of liver disease may lead to a different or additional laboratory evaluation rather than an evaluation for VWD (see II.B., below).

2. Evaluation by Laboratory Testing

• Initial laboratory evaluation for the etiology of a bleeding disorder should include:
  • A complete blood count (CBC including platelet count), prothrombin time (PT), activated partial thromboplastin time (PTT), and optionally either thrombin time or fibrinogen level.
  • If laboratory abnormalities besides the PTT are present (the platelet count may also be decreased in type 2B VWD), in conjunction with the history and physical examination findings, consider bleeding disorders other than VWD or additional underlying diseases.
  • If the mucocutaneous bleeding history is strong, consider performing initial VWD assays at the first visit (see II.B., below).
  • If there are no abnormalities on initial blood testing, or if there is an isolated prolonged PTT that corrects on the 1:1 mixing study, the following three tests for VWD should be performed (II.B., below), unless another cause for bleeding has been identified and VWD is not likely (see Figure 4). For further laboratory evaluation, physicians may consider referral to a hemostasis center because of the special sample handling and testing requirements (see Table 10). 
  • Grade C, level IV
• Initial tests for diagnosing or excluding VWD include the following three tests:
  • VWF:RCo
  • VWF:Ag
  • Factor VIII activity 
  • Grade B, level III3,43,175,176See Evidence Table 2.
• If any one of the above test results is abnormally low, a discussion with or a referral to a hemostasis expert is appropriate. In addition to repeating the initial three tests (in most cases), the specialist may recommend appropriate studies from the following:
  • The first set of additional tests may include:
    • Evaluation of the ratio of VWF activity (VWF:RCo and/or VWF:CB) to VWF antigen (only in laboratories that have defined reference ranges for the ratio[s]) Grade B, level III70,71,91,163,175,190See Evidence Table 3.
    • VWF multimer study 
    • Grade B, level III181
    • Ristocetin—induced platelet aggregation 
    • Grade B, level III46
    • VWF collagen binding activity (VWF:CB) 
    • Grade B, level IIb175,185,186See Evidence Table 4.
  • Studies in selected patients, especially those who have discordantly low FVIII activity compared to VWF levels and who are suspected of having type 2N VWD, should include a FVIII binding assay (VWF:FVIIIB) Grade B, level IIb77,78,188See Evidence Table 5.
  • Additional studies in selected persons may include:
    • Gene sequencing 
    • Grade C, level IV
    • Assays for antibodies to VWF 
    • Grade C, level IV
    • Platelet—binding studies 
    • Grade B, level III182

3. Making the Diagnosis

• Clinical criteria.Clinical criteria. These criteria include personal and/or family history and/or physical evidence of mucocutaneous bleeding. Until further validation of scoring systems and criteria for assessing bleeding history and the probability of VWD, especially type 1 VWD, the Expert Panel suggests that an increasing number of positive responses to the questions about bleeding (Figure 3, and Box 1) and abnormal findings on physical examination increase the likelihood that an individual has a bleeding disorder, including possible VWD. 
• AND
• Laboratory criteria. The values in the following table represent prototypical cases without additional VWF (or other disease) abnormalities in the patient. In practice, exceptions occur, and repeat testing and clinical experience are important and may be necessary for interpretation of laboratory results.
  • Although published evidence is limited, for defining the ratio of VWF:RCo/VWF:Ag to use for distinguishing type 1 VWD versus type 2 VWD variants (A, B, or M), the Expert Panel recommends a ratio of <.5-0.7 until more laboratories clearly define a reference range using large numbers of normal subjects and persons who have type 1 VWD and type 2 VWD variants. 
  • Grade C, level IV70,71,91,163,189,190
  • The panel currently recommends that 30 IU/dL be used as the "cut—off" level for supporting the definite diagnosis of VWD for the following reasons:
    • There is a high frequency of blood type O in the United States, and it is associated with "low" VWF levels;43
    • Bleeding symptoms are reported by a significant proportion of normal individuals;137-140 and
    • No abnormality in the VWF gene has been identified in many individuals who have mildly to moderately low VWF:RCo levels 
    • Grade C, level IV100-102
• This recommendation does not preclude the diagnosis of VWD in individuals with VWF:RCo of 30-50 IU/dL if there is supporting clinical and/or family evidence for VWD. This recommendation also does not preclude the use of agents to increase VWF levels in those who have VWF:RCo of 30-50 IU/dL and may be at risk for bleeding.

? refers to a decrease in the test result compared to the laboratory reference range. 
* <IU/dL is designated as the level for a definitive diagnosis of VWD; there are some patients with type 1 or type 2 VWD who have levels of VWF:RCo and/or VWF:Ag of 30-50 IU/dL. 
? The VWF:Ag in the majority of individuals with type 2A, 2B, or 2M VWD is <50 IU/dL.

Introduction

Therapies to prevent or control bleeding in persons who have VWD follow three general strategies. The first strategy is to increase plasma concentration of VWF by releasing endogenous VWF stores through stimulation of endothelial cells with DDAVP. The second approach is to replace VWF by using human plasma-derived, viral-inactivated concentrates. The third strategy employs agents that promote hemostasis and wound healing but do not substantially alter the plasma concentration of VWF. The three treatment options are not mutually exclusive, and patients may receive any one or all three classes of agents at the same time. The appropriateness of therapeutic choice is dependent on the type and severity of VWD, the severity of the hemostatic challenge, and the nature of the actual or potential bleeding. Because some persons who have VWF:RCo >30 IU/dL manifest clinical bleeding, persons not having a definite diagnosis of VWD but who have low VWF and a bleeding phenotype may merit treatment or prophylaxis of bleeding in certain clinical situations.196 Infusions of VWF to prevent bleeding episodes—known as prophylaxis—are less frequently required in patients who have severe VWD in contrast to patients who have severe hemophilia. The CDC Universal Data Collection Project Web site (http://www2a.cdc.gov/ncbddd/htcweb/) reports that 45 percent of patients who have severe hemophilia A use some type of prophylaxis, either continuous or intermittent, compared with 10 percent of patients who have severe VWD. Risks and benefits of prophylaxis should be carefully weighed when considering long-term therapy for VWD.211,212 Treatment of VWD in the United States varies widely and frequently is based on local experience and physician preference. Few standard recommendations exist to guide therapy for VWD.6,7,9 This guidelines document presents recommendations regarding the management and prevention of bleeding in persons who have VWD and reviews the strength of evidence supporting those recommendations.

Therapies To Elevate VWF: Nonreplacement Therapy

DDAVP (Desmopressin: 1-desamino-8-D-arginine vasopressin)

Mechanism of action of DDAVP. DDAVP is a synthetic derivative of the antidiuretic hormone, vasopressin. DDAVP has been used to treat VWD for 25 years, and its pharmacology, mechanism of action, and indications have been reviewed extensively.213-215 DDAVP stimulates the release of VWF from endothelial cells through its agonist effect on vasopressin V2 receptors.213,214,216 The mechanism by which DDAVP increases plasma concentration of VWF is probably through cyclic AMP-mediated release of VWF from endothelial cell Weibel-Palade bodies.216,217 FVIII levels also increase acutely after administration of DDAVP, although the FVIII storage compartment and the mechanism of release by DDAVP have not been fully elucidated to date.11,218 DDAVP induces the release of tissue plasminogen activator (tPA).219,220 However, the secreted tPA is rapidly inactivated by plasminogen activator inhibitor (PAI-1) and does not appear to promote fibrinolysis or bleeding after DDAVP treatment.

DDAVP dosing and administration. Table 11 displays published reports of DDAVP effects on laboratory assays of VWF and FVIII in normal persons and persons who have various subtypes of VWD.64,92,99,221-232 When administered intravenously to normal persons as well as to patients who have VWD or mild hemophilia, DDAVP consistently increases plasma VWF and FVIII from twofold to greater than fivefold over baseline levels.92,218,223,225-227,230,231 Children under the age of 2 have a significantly lower response rate than older children.230 Two controlled prospective studies in healthy volunteers form the basis for DDAVP dosing recommendations.225,227 Maximal FVIII response was determined at 0.3 micrograms/kilogram in both studies, while maximal VWF release data were determined at 0.2 and 0.3 micrograms/ kilogram in the two studies, respectively. Based on these data, standard dosing of DDAVP is 0.3 microgram/kilogram given intravenously in 30-50 mL of normal saline over 30 minutes, with peak increments of FVIII and VWF 30 to 90 minutes postinfusion.218,223,225,233 Nasal administration of high-dose desmopressin acetate (Stimate®) is often effective for minor bleeding, but intravenous administration is the preferred route for surgical bleeding prophylaxis and for treatment of major hemorrhage.

A retrospective review of DDAVP administration to 56 children who had nonsevere type 1 VWD found a 91 percent response rate, defined as FVIII and VWF activity increase of twofold, to at least 30 IU/dL.230 In a small case series of VWD patients, the consistency of FVIII increases and the response of the bleeding time after a second test dose of DDAVP was within 10-20 percent of the initial value.231 Evidence shows that response to DDAVP diminishes with repeated doses, probably due to depletion of the VWF storage compartment.218,227 However, when DDAVP was given in four daily doses to 15 patients who had type 1 VWD, an increase in FVIII activity of at least twofold was found in 100 percent of the patients after the first administration, in 80 percent after the second, in 87 percent after the third, and in 74 percent after the fourth administration.226

Consistency of response to DDAVP has been studied using 24-hourly dosing for three to four daily doses.226,227 A series of 15 type 1 VWD patients showed a mean rise of VWF:RCo to fivefold above baseline following the first dose of DDAVP, significantly decreased response to fourfold following the second daily dose, and no significant change in response among the second to fourth doses.226 The proportion of VWD patients attaining at least a twofold rise in FVIII activity following the second to fourth daily doses—80 percent following the second daily dose of DDAVP to 74 percent following the fourth dose—was substantially higher than that for hemophilia A patients (55 to 37 percent). There is no published evidence regarding response to DDAVP given every 12 hours to compare with daily dosing of DDAVP. In addition to tachyphylaxis, hyponatremia may complicate repeated DDAVP dosing, and fluid restriction as well as serum sodium monitoring are recommended.

DDAVP can also be administered subcutaneously or intranasally.225,227,233 The effective subcutaneous dose is identical to intravenous dose, but the subcutaneous preparation is not available in the United States. The preparation of DDAVP for nasal instillation (Stimate®) contains 150 micrograms per metered nasal puff (0.1 mL of a 1.5 mg/mL solution). The dose is one puff for persons who weigh <50 kg and two puffs (one to each nostril) for persons weighing 50 kg or more. Although the intra- and intersubject coefficient of variation for reproducibility of nasal spray effect is good, nasal absorption is variable, and all patients who have VWD and are responsive to intravenous DDAVP should undergo a trial of Stimate® to measure FVIII and VWF response before using it.225 When used for epistaxis, Stimate® ideally is delivered into the nonbleeding nostril. Persons who have inadequate plasma responses to intravenous DDAVP will not respond to Stimate®.

There is also a nasal formulation of DDAVP (for enuresis) that contains 10 micrograms per puff (about 7 percent of the Stimate® concentration); however, this preparation is not suitable for treatment of VWD. Patients and parents must be carefully instructed regarding the two concentrations of nasal DDAVP—the one used for bleeding (1.5 mg/mL), and the one used for antidiuretic hormone replacement (diabetes insipidus) and bedwetting (0.1 mg/mL)—to avoid accidental underdosing for VWD.

Monitoring of VWD patients receiving DDAVP. Treatment of patients who have VWD with DDAVP should be based on results of a therapeutic trial, ideally one performed in a nonbleeding state and before clinical use.

Although the pattern of DDAVP responsiveness is fairly consistent within VWF subtypes, population results should not be used to plan treatment of individual patients (see Table 11). VWF:RCo and FVIII activities should be measured in all VWD patients at baseline and within 1 hour after administering DDAVP. Additional assay of VWF:RCo and FVIII, 2-4 hours after DDAVP, will evaluate for shortened survival and should be considered for patients who have a history of poor response to treatment.41

According to conservative definitions of laboratory response, the majority of patients who have type 1 VWD respond adequately to DDAVP (Table 11). Single infusions of DDAVP for common bleeding episodes—such as epistaxis, simple dental extraction, or menorrhagia—do not usually require laboratory monitoring. Patients should be monitored for VWF:RCo activity as well as FVIII activity around major surgeries or major bleeding events. For major surgeries or bleeding events, patients who have VWD should be referred to hospitals with in-house or daily laboratory availability of FVIII and VWF:RCo activity assays. Care should be taken to monitor serum electrolytes, especially after surgery or multiple doses of DDAVP. Adult patients, especially those who are elderly, should be evaluated for CVD before using DDAVP because myocardial infarction rarely has been precipitated by DDAVP therapy in patients who have hemophilia or uremia.234-236

Table 11. Intravenous DDAVP Effect on Plasma Concentrations of FVIII and VWF in Normal Persons and Persons Who Have VWD

* Data are given as mean fold increase in plasma factor compared to baseline after a single administration of DDAVP. Mean fold increases were calculated from original data, where possible, if not included in the manuscript. 
† Response defined as twofold increase AND to at least 30 IU/dL VWF:RCo and FVIII. 
FVIII, factor VIII (8); N/A, not available; VWF:Ag, VWF antigen; VWF:RCo, von Willebrand factor (VWF) ristocetin cofactor.

Pharmacokinetics of VWF and FVIII after DDAVP. After stimulation with DDAVP, released VWF and FVIII circulate with an apparent half-life characteristic of the patient's own proteins, or approximately 8-10 hours for both proteins in normal individuals.218 Type 2 VWF proteins that are released by DDAVP will increase in concentration but retain their intrinsic molecular dysfunction.237 For this reason, DDAVP has been efficacious in only a minority of patients who have types 2A or 2M VWD. Therefore, monitoring is necessary to document adequate correction of VWF:RCo. Type 2N VWF lacks FVIII stabilization; consequently, patients who have 2N VWF will release FVIII and the abnormal VWF protein as expected, but the survival of released FVIII may be severely decreased, with an apparent plasma half-life as low as 2 hours, depending on the mutation.168,228 Emerging information suggests that some individuals who have type 1 VWD have accelerated plasma clearance of VWF and may benefit from trial testing of VWF:RCo 2-4 hours after a dose of DDAVP.40,238

Following infusion of DDAVP into patients with type 2B VWD, VWF multimers of larger but still somewhat less than normal molecular weight can be detected in plasma after 15 to 30 minutes, with persistence throughout 4 hours of study.63,168,237,239 Although formal pharmacokinetic studies have not been reported for type 2B VWD, VWF:RCo activity increases were less than that seen in type 1 VWD with an apparent half-life of approximately 4 hours.63,229 Bleeding time response to DDAVP in type 2B VWD is inconsistent.222,229

Clinical response to DDAVP in VWD. The clinical effectiveness of DDAVP to prevent or control bleeding depends, in large part, on the plasma VWF:RCo or FVIII activity achieved after drug administration, which in turn depends primarily on the basal levels of plasma FVIII and VWF:RCo and to a lesser extent on the underlying qualitative VWF defect.64,92,99,221-232 Table 12 and Evidence Tables 7-12 summarize published data on clinical response when using DDAVP in conjunction with common surgical procedures.136,218,221-223,230,232,240-250 All data were derived from retrospective studies and small case series; there are no randomized clinical trials of the use of DDAVP in persons who have VWD.

Whether DDAVP will be adequate for prophylaxis around surgery or for treatment of bleeding events in persons who have type 1 VWD is dependent on the severity of the hemostatic challenge and the time required for healing. Major surgery requires hemostasis for 7-14 days,247,251-256 whereas minor surgeries can be treated adequately in 1-5 days.243,244,247,256 If treatment is necessary for more than 3 days, VWF concentrate is usually given to supplement therapy with DDAVP.244,247 Currently, however, expert opinions are divided regarding the risk of delayed hemorrhage 5-10 days after a bleeding challenge in VWD patients, e.g., those who have had tonsillectomy or given birth. In small case series, persons who have type 1 VWD Vicenza manifest an exaggerated response to DDAVP.41,92,231 Individuals who have type 2N VWD exhibit a brisk rise in plasma FVIII after receiving DDAVP, but they have a mean FVIII half-life of only 3 hours because of deficient FVIII stabilization by the defective VWF.228 Persons who have low platelet VWF or type 2A VWD have a low likelihood of having a clinically relevant DDAVP response, but they may warrant a DDAVP trial.224,231 Type 2B VWD previously was a contraindication to DDAVP therapy because platelet counts usually fell after DDAVP stimulation.257 However, thrombocytopenia after DDAVP in type 2B VWD is usually transient and often is not associated with bleeding or thrombosis.258 In patients who have type 2B VWD, decrease in platelet count after DDAVP administration has been considered "pseudothrombocytopenia" by some authors because it is related to platelet agglutination in vitro rather than in vivo agglutination and clearance.63,239 Therefore, DDAVP may be cautiously considered for patients who have type 2B VWD. Patients who have type 3 VWD almost never experience a clinically relevant rise in VWF:RCo or FVIII activities, and DDAVP is not considered clinically useful in these patients.224,230

Complications and toxicities of DDAVP. Minor side effects of DDAVP are common and include facial flushing, transient hypertension or hypotension, headache, or gastrointestinal upset,214,215,262 but these effects rarely limit clinical use. Water retention after a dose of DDAVP, with an increase in urinary osmolality, is universal; however, decreased serum sodium in otherwise healthy adults is variable and is related to multiple doses.262,263 In the case of repeated dosing, all patients should be instructed to limit fluid intake to maintenance levels for 24 hours.264-266 Prophylactic use of DDAVP complicates the management of fluids and electrolytes for surgery or during childbirth. Seizures have been associated with hyponatremia after DDAVP administration, primarily in young children.263,266 Most pediatric hematologists do not use DDAVP in children under the age of 2 years.230,261,266

Myocardial infarction after treatment with DDAVP has been reported, although rarely, in patients who have mild hemophilia A.234,236,267 DDAVP should be avoided in patients who are at very high risk for cardiovascular or cerebrovascular disease, especially the elderly, as underlying inhibition of plasminogen activation with DDAVP-related vasoconstriction contributes additional prothrombotic effects in these patients.268 Because of reported complications in other patient populations, DDAVP should be used with caution for brain, ocular, and coronary artery surgeries,235,269,270 and VWF concentrate replacement generally is used in these settings. DDAVP does not appear to increase myometrial contractility significantly; consequently, pregnancy is not an absolute contraindication271-274 but use of DDAVP is rarely indicated (see "Pregnancy").

Table 12. Clinical Results of DDAVP Treatment in Patients Who Have VWD*

DDAVP, 1-desamino-8-D-arginine vasopressin (desmopressin, a synthetic analog of vasopressin) 
* For additional detail and information, see Evidence Tables 7-11. 
† NA, not available

Therapies To Elevate VWF: Replacement Therapy

As of January 2007, Humate-P® and Alphanate SD/HT® are the only plasma-derived concentrates licensed in the United States to replace VWF in persons who have VWD. One other plasma derivative—Koate DVI®—is licensed in the United States to treat hemophilia and has been used off-label for VWD. These products are not identical, have differing ratios of FVIII to VWF, and should not be considered as interchangeable.275-277 All of these products are manufactured at U.S.-licensed facilities from pooled plasma collected from paid donors.

Products that contain FVIII and little or no VWF are generally not useful to treat VWD, but in rare circumstances these products may be used to treat patients who have antibody-mediated AVWS.278 These products include the plasma-derived concentrates Monoclate P®, Monarc M®, and Hemofil M®; and recombinant products Helixate FS®, Kogenate FS®, Recombinate®, Advate®, and ReFacto®.

Humate-P®, a lyophilized concentrate of purified VWF and FVIII, contains other plasma proteins including fibrinogen and albumin. In Humate-P®, the quantity of the large, most hemostatically active multimers of VWF is decreased compared to fresh plasma.279 When reconstituted at the recommended volume, each milliliter of the product contains 50-100 IU/mL VWF:RCo and 20-40 IU/mL FVIII activity (Humate-P® package insert). The median half-life of VWF:RCo activity was 10.3 hours (range: 6.4-13.3 hours) in one study (see package insert) and 11.3 hours in another study.251 The product is indicated for use in adult and pediatric patients for treatment of spontaneous and trauma-induced bleeding when use of DDAVP is thought or known to be inadequate or contraindicated. Humate-P® has received FDA approval for use in prophylactic management of surgery and invasive procedures in patients with VWD.

Alphanate SD/HT® is a lyophilized concentrate of VWF and FVIII, and other plasma proteins. It is prepared from pooled human plasma by cryoprecipitation of FVIII, fractional solubilization, and further purification employing heparin-coupled, cross-linked agarose. Upon reconstitution to the recommended volume, each milliliter of product contains 40-180 IU/mL FVIII activity, and not less than 16 IU/mL VWF:RCo activity (Alphanate SD/HT® package insert). The median half-life for VWF:RCo activity was 6.91 hours (mean: 7.46 +/- 3.20 hours; range: 3.68 to 16.22 hours. Package Insert). The product is indicated for surgical and/or invasive procedures in patients with VWD in whom either DDAVP is ineffective or contraindicated. It is not indicated for patients with severe VWD (type 3) undergoing major surgery.

Adverse reactions are rare but include allergic and anaphylactic symptoms, urticaria, chest tightness, rash, pruritus, and edema.253 If these reactions occur, the infusion should be stopped, and appropriate treatment should be given as required. The product should be used with caution in patients who have known risk factors for thrombosis, as there have been a few reports of venous thromboembolism associated with high levels of FVIII.280,281 Risk factors include old age, previous thrombosis, obesity, surgery, immobility, hormone replacement therapy (HRT), and use of antifibrinolytic therapy. If patients receive VWF replacement therapy continuously for several days, it has been recommended that FVIII levels be monitored to avoid unacceptably high levels.215,281

The products that contain VWF:RCo activity differ significantly in their ratios of VWF:RCo to FVIII252,282,283 and one should not assume that the dose or frequency of dosing is the same for all. The ratio of VWF:RCo to FVIII for Humate-P® in various reports is 2.7, 2, and 1.6; for Koate DVI®, the ratio is 1.2 and 0.8; and for Alphanate®, the ratio is 0.5.251 These products also differ in their relative levels of high-molecular-weight multimers. Koate DVI®, in particular, has fewer large VWF multimers compared to Alphanate SD/HT®, which has fewer than Humate-P® or normal plasma.277,284,285

Cryoprecipitate, derived from plasma, historically has been used to treat hemophilia A and VWD. Although cryoprecipitate is not required to have a specified level of VWF, the final product must have on average at least 80 units of FVIII per standard donor unit.286 Currently, cryoprecipitate is used under rare circumstances to treat VWD, such as when potential exposure to infectious agents can be limited by using directed donations to prepare the product.287 However, the use of cryoprecipitate is strongly discouraged by the National Hemophilia Foundation, except in life-or limb-threatening situations when no VWF concentrate is available, because cryoprecipitate is not virally inactivated.288 In developing countries, patients who have VWD may have no other options, because virally inactivated plasma concentrates are not available or are too expensive,283 but use of cryoprecipitate poses a significant risk of transmitting disease.289

VWF concentrates are dosed primarily on the basis of labeled VWF:RCo units and secondarily on the basis of labeled FVIII units. A dosing trial with pharmacokinetic laboratory monitoring should be considered before major surgery for selected patients with type 3 VWD or AVWS who are at risk for poor VWF recovery because of inhibitors. Use of VWF concentrates to prevent or control bleeding has been clinically efficacious, as shown on Table 13. The ultimate goal of surgical prophylaxis is to achieve a therapeutic level of 100 IU/dL VWF:RCo and, at least for the first 3 days of treatment, a nadir of 50 IU/dL VWF:RCo, as well as similar targets for FVIII.251,253-256,290 Successful surgical hemostasis was reported with the use of continuous infusion after initial bolus infusion at rates of 1-2 U/kg/hr VWF:RCo.252

Replacement therapy, using a VWF concentrate, is indicated for significant bleeding events or major surgery in patients who have types 2 and 3 VWD as well as in patients who have type 1 VWD and are unresponsive to DDAVP or require a protracted duration of therapy, or where DDAVP is contraindicated (see above). The dose and duration of therapy are dependent on the hemostatic challenge and expected duration required for hemostasis and wound healing. Major surgery requires hemostasis for 7-14 days,247,251-256 whereas minor surgeries can be treated adequately in 1-5 days.243,244,247,256 Certain procedures can be managed adequately by using a single infusion of 20-40 U/kg VWF:RCo before the procedure. Table 14 lists examples of major and minor surgical procedures. Table 15 lists initial dosing recommendations for use of VWF replacement therapy to prevent or treat bleeding. These recommendations are based on published results (see Table 13) as well as consensus expert opinion. The adequacy of courses of VWF replacement usually should be confirmed by laboratory assessment of VWF:RCo and FVIII levels, although monitoring of single infusions for treatment of outpatients may not be necessary. Duration of VWF elevation after replacement therapy is highly variable in the surgical setting. Thromboembolic events have been reported in patients who have VWD and are in situations of high thrombotic risk and receiving VWF:RCo/FVIII complex replacement therapy, especially in the setting of known risk factors for thrombosis.280-282 In all patients who have VWD and are receiving VWF concentrate, attention should be given to avoid exceeding maximal recommended levels of VWF:RCo and FVIII activities (see Recommendation VII.D, below), perform proper thrombotic-risk assessment, and institute appropriate preventive strategies. Recombinant VWF has been prepared and evaluated in animal models292 but is not available for use in humans.

Human platelets contain 10-15 percent of total blood VWF and platelet transfusions have been used successfully to treat bleeding in VWD patients.293,294 Platelet transfusion therapy should be considered as an adjunctive source of VWF, especially in patients with type 3 or platelet low VWD and platelet-type VWD, to control bleeding that is non- or poorly responsive to replacement therapy with VWF concentrate.

Table 13. Efficacy of VWF Replacement Concentrate for Surgery and Major Bleeding Events*

* For additional detail and information, see Evidence Table 12. 
† Loading dose (VWF:RCo IU/dL) reported as median except for Lubetsky (mean). 
? Indicates that continuous infusion was used after the loading dose. 
§ Loading dose (FVIII IU/dL).

Table 14. Suggested Durations of VWF Replacement for Different Types of Surgical Procedures

*Individual cases may need longer or shorter duration depending on the severity of VWD and the type of procedure.

Table 15. Initial Dosing Recommendations for VWF Concentrate Replacement for Prevention or Management of Bleeding

*Loading dose is in VWF:RCo IU/dL.

Other Therapies for VWD

Antifibrinolytics. The antifibrinolytic drugs aminocaproic acid and tranexamic acid are agents that inhibit the conversion of plasminogen to plasmin, inhibiting fibrinolysis and thereby helping to stabilize clots that have formed. Studies in hemophilia and in prostatectomy provided the basis for initial trials of antifibrinolytic agents in VWD.295 The drugs can be used orally or intravenously to treat mild mucocutaneous bleeding in patients who have VWD. In patients who have mild to moderate VWD, tranexamic acid given topically in the oral cavity ("swish and swallow or spit") every 6 hours has been used for prophylaxis in dental surgery, in combination with applied pressure, other topical agents, and suturing of surgical sites.242 The evidence for the effectiveness of local application of these agents is based on clinical case series,296 but this route of administration is not currently approved by the U.S. Food and Drug Administration (FDA). When DDAVP and/or VWF/FVIII concentrates are indicated, the use of antifibrinolytic agents as adjuncts to DDAVP or VWF concentrates has been helpful in controlling bleeding, such as in the oral cavity36,221,223,232,242,246-248 and in the gastrointestinal and genitourinary tracts.

The usual adult dose of aminocaproic acid is 4-5 g as a loading dose orally or intravenously (1 hour before invasive procedures), and then 1 g per hour, intravenously or orally, or 4-6 g every 4-6 hours orally, until bleeding is controlled, or for 5-7 days postoperatively.215 Total daily dose of aminocaproic acid is limited to 24 g per 24 hours to minimize potential side effects. Weight-based dosing is required in children and can also be used in adults (50-60 mg/kg).215,296 Lower doses (25 mg/kg) may be effective and can be used when gastrointestinal side effects interfere with therapy. Tranexamic acid is given intravenously at a dose of 10 mg/kg every 8 hours.215 The oral form is not currently available in the United States, and use of the intravenous form as an oral rinse ("swish and swallow" approach) is not an FDA-approved indication. The package insert for each drug should be consulted for more detailed guidance and for a full list of risks and contraindications. Both drugs can cause nausea and vomiting; less frequent but serious side effects include thrombotic complications. Both drugs are excreted renally, and dose adjustment or avoidance is advisable when significant renal insufficiency is present. Disseminated intravascular coagulation (DIC) and/or bleeding from the renal parenchyma or upper urinary tract are relative contraindications to antifibrinolytic agents. Renovascular thrombi have followed use of fibrinolytic agents in patients with DIC and have caused renal failure. Patients have also experienced urinary tract obstruction with upper urinary tract bleeding related to large clots in the renal pelvis or lower urinary tract. Changes in color vision during therapy with tranexamic acid require cessation of the drug and ophthalmologic examination.

Topical agents. Topical bovine thrombin (Thrombin-JMI) is marketed in the United States as an aid to hemostasis for topical therapy of accessible minor bleeding from capillaries and small venules. Fibrin sealant (Tisseel VH®, consisting of human thrombin, fibrinogen concentrate, and bovine aprotinin) is indicated as an adjunct to hemostasis in certain surgical situations, but it is not effective for the treatment of massive and brisk arterial bleeding. Fibrin sealants have been used with good results as adjunctive therapy for dental surgery in persons who have hemophilia or VWD.242,297 Topical collagen sponges are also approved for control of bleeding wounds.298 Other topical agents approved for limited indications include Coseal®, Bioglue®, and Quickclot®; however, no reports of their use in treating VWD could be found. Quickclot®, containing the mineral zeolite, was approved recently for use with compression dressings for control of external traumatic bleeding in the prehospital setting (e.g., battlefield). The added benefit of topical agents—when used with single or combination therapies including antifibrinolytic drugs, DDAVP, and VWF/FVIII concentrate—is unproven. The topical use of plasma-derived bovine or human proteins imparts a theoretical risk of disease transmission and of potential allergic and other immune reactions. The use of fibrin sealants in addition to drugs and/or concentrates may be viewed as optional adjunctive therapy for dental surgery and for cases in which surface wound bleeding continues despite combined therapy with drugs and concentrates. The safety of these topical agents in therapy for VWD remains to be demonstrated.

Other Issues in Medical Management

All persons who have significant bleeding symptoms related to VWD are likely to require human blood product administration and should receive immunizations for hepatitis A and B as recommended for individuals with hemophilia.299 Persons who have VWD should be counseled to avoid aspirin, other NSAIDs, and other platelet-inhibiting drugs.300-302

Treatment of AVWS

In an international registry of 189 cases of AVWS, DDAVP produced clinical and laboratory improvement in one-third of cases, although this effect was often short lived.117 If FVIII activity and the PTT were abnormal, a good DDAVP response was less common than in hereditary VWD and was often brief. In the international registry series, most patients who had AVWS also received VWF/FVIII concentrates; the extent and duration of response was varied. Therefore, VWF:RCo and FVIII levels must be measured pre- and postinfusion of DDAVP or VWF/FVIII concentrates in patients who have AVWS to determine the extent and duration of response and to guide subsequent dosage and dosing intervals.117,157

In patients who had a previous inadequate response to DDAVP and VWF/FVIII concentrates, intravenous immunoglobulin G (IGIV; 1 g/kg daily for 2 days) given alone was effective in controlling bleeding and raising VWF:RCo activity for 3 weeks in all eight patients who had excessive bleeding and an IgG-monoclonal gammopathy of uncertain significance (MGUS).303 In the international registry series, one-third of the 63 patients treated with high-dose IGIV had a good response.117 The underlying diagnoses of the responders were lymphoproliferative disorders (including MGUS), solid tumors, and autoimmune diseases. An anti-VWF antibody could be demonstrated in vitro in about two thirds of those responders. High dose IGIV therapy in the setting of AVWS is an off-label use but should be considered when DDAVP and VWF/FVIII concentrate therapy fail to control bleeding symptoms adequately.304-306 Some patients who have immune-mediated AVWS have responded to plasmapheresis, corticosteroids, and immunosuppressive agents.117 Because many patients in the international registry series received multiple therapeutic modalities, the independent contribution of each therapy to clinical improvement was unclear.

When all other therapeutic modalities fail to control bleeding adequately, the infusion of recombinant FVIIa may be considered, but this agent should be used with caution. Little experience has been reported for its use in treating VWD. A recent report described acute myocardial infarction immediately after the second dose of 90 microgram/kilogram in a 50 year old man who had hereditary type 2A VWD, gastrointestinal bleeding, and several risk factors for, but no history of, coronary artery disease.307

Cardiac Valvular Diseases. Congenital or acquired heart disease has been associated with AVWS.117,119,308 Elevated shear stress around a stenotic valve or septal defect may promote the proteolysis and depletion of high-molecular-weight VWF multimers.134 Patients who had associated aortic stenosis or other cardiac valvular disorders infrequently responded to any of the therapies described above.117,122 After surgical correction of the cardiac defect, the multimer pattern has improved at least transiently in most patients studied.119,122,308 Administration of VWF/FVIII concentrate immediately preoperatively should be considered for patients who demonstrate transient improvement in VWF activity with a test dose.

Angiodysplasia. Bleeding from gastrointestinal angiodysplasia has been reported in persons who have AVWS309 as well as in persons who have various types of congenital VWD. For example, bleeding from angiodysplasia is a classic presentation of AVWS associated with aortic stenosis122,310 and is often resistant to medical therapy, requiring surgical correction of the valve defect to ameliorate bleeding symptoms. In the absence of a correctable underlying etiology of angiodysplasia and bleeding associated with AVWS or congenital VWD, management of the condition can be challenging, as no single treatment modality is successful in all cases.311

Thrombocytosis. Thrombocytosis, especially in persons who have essential thrombocythemia, is associated with a relative reduction in the proportion of high-molecular-weight multimers.125 Although the relation of this abnormality to bleeding is inconsistent, treatment is aimed at reduction of the platelet count.

Hypothyroidism. In contrast to the above syndromes, AVWS that occurs in hypothyroidism is caused by decreased synthesis, and the VWF multimer patterns are normal.312,313 A minority of patients who have hypothyroidism have VWF levels below normal, and not all who have low VWF levels have bleeding symptoms. The decrease in VWF is corrected by thyroid hormone replacement.127,313

Management of Menorrhagia in Women Who Have VWD

Menorrhagia is often the primary bleeding symptom in women who have VWD.85,314,315 Menorrhagia, however, may be a sign of a gynecological disorder rather than VWD.316 Therefore, a full gynecological evaluation is required before therapy is initiated.316

Medical therapies that have been described to control menorrhagia in women who have VWD include combined oral contraceptives, tranexamic acid, DDAVP, and, most recently, the levonorgestrel-releasing intrauterine system (Table 16). Data regarding the effectiveness of these therapies are limited. The only published randomized clinical trial of DDAVP for menorrhagia was small and failed to demonstrate efficacy compared to placebo.317 The available data show no evidence that DDAVP is more effective than other therapies used to treat menorrhagia.318 Depending on the woman's age, underlying gynecologic condition, and reproductive plans, any of the therapies demonstrated to be effective for the treatment of menorrhagia in women without VWD may be suitable, with the exception of NSAIDs, which decrease platelet function and systemic hemostasis.319 In one retrospective review of 36 adolescent girls with VWD and menorrhagia, treatment using oral contraceptive pills (OCPs) or intranasal DDAVP were equally efficacious.320

Table 16. Effectiveness of Medical Therapy for Menorrhagia in Women Who Have VWD

In the adolescent or adult female who does not desire pregnancy, but may desire future childbearing, the first choice of therapy should be combined oral contraceptives. Combined oral contraceptives contain a synthetic estrogen (ethinyl estradiol) and a progestin.328 The progestin prevents ovulation, and the synthetic estrogen prevents breakthrough bleeding.329 A majority of studies have found that combined oral contraceptives increase fibrinogen, prothrombin, factor VII, FVIII, and/or VWF330-332 and, consequently, promote hemostasis. It is not known whether the increase in coagulation factors associated with combined oral contraceptives contributes to the clinical response, but combined oral contraceptives do reduce menstrual blood loss333 and increase hemoglobin concentrations in women who have anemia.334-336 Combined oral contraceptives, used by tens of millions of women for prolonged periods of time, have been proven to be safe for long-term use337 except in women with thrombophilia.329 Although no formal studies of the effects of the contraceptive patch on hemostasis have been performed, the patch likely has effects similar to those of combined oral contraceptives.338

For a woman who has VWD and would otherwise be a suitable candidate for an intrauterine device, the second choice of therapy should be the levonorgestrel-releasing intrauterine system. The levonorgestrel-releasing intrauterine system is a progestin-impregnated intrauterine device that is believed to reduce menstrual blood loss by opposing estrogen induced growth of the endometrium or lining of the uterus.339

Women who do not respond to hormonal therapy and are being considered for treatment with DDAVP or VWF concentrate should be referred to a hemophilia treatment center or to a hematologist who has expertise in hemostasis. Treatments specific for VWD (such as DDAVP or VWF concentrate), or antifibrinolytic therapy, although they have not been proven to be effective for menorrhagia, may be tried.

In addition to medical therapies, surgical therapies have been used to treat menorrhagia in women who have VWD. Dilation and curettage (D & C), while occasionally necessary to diagnose intrauterine pathology, is not effective in controlling heavy menstrual bleeding.323 In two cases reported by Greer et al.323 and two cases reported by Kadir et al.,340 D & C resulted in further blood loss.

Endometrial ablation, on the other hand, reduced menstrual blood loss in seven out of seven women who had VWD.341 Three, however, ultimately required hysterectomy, compared to 12-34 percent of women who did not have VWD who usually require hysterectomy.342-346 Women who have VWD and undergo hysterectomy may be at greater risk of perioperative bleeding complications than other women, and bleeding may occur despite prophylactic therapy.137,315 Hysterectomy carries the risk of bleeding complications, but women who require the operation should not be deprived of its benefits. Because menorrhagia is often the primary bleeding symptom experienced by a woman who has VWD, hysterectomy offers the possibility of the elimination of bleeding symptoms for menorrhagia and significant improvement in quality of life.345,347,348

Hemorrhagic Ovarian Cysts

There are multiple case reports of women who have VWD and have experienced hemorrhagic ovarian cysts.322,323,349-353 Silwer, for example, reported that 9 of 136 (6.8 percent) women who had VWD experienced this problem.137 Ovulation is not normally accompanied by any significant bleeding, but in a woman who has a congenital bleeding disorder such as VWD, the potential exists for bleeding into the peritoneal cavity or bleeding into the residual follicle, resulting in a hemorrhagic ovarian cyst352 or retroperitoneal hematoma.323 Acute treatment of hemorrhagic ovarian cysts with surgical therapy, tranexamic acid, and factor replacement has been reported.323,351,352 Oral contraceptives have been used to prevent recurrences.349,350,352

Pregnancy

Few options are available for the management of menorrhagia or recurrent hemorrhagic ovarian cysts in women who have VWD and desire pregnancy. Although data are limited to case reports, DDAVP, antifibrinolytics, or VWF concentrate may be tried.322

Ideally, planning for pregnancy begins before conception. Women who have VWD and are contemplating a pregnancy should be aware that they may be at an increased risk of bleeding complications during pregnancy354 and are definitely at increased risk of postpartum hemorrhage.145 Before conception or during pregnancy, women should be offered the opportunity to speak with a genetic counselor regarding the inheritance of VWD355 and with a pediatric hematologist regarding the evaluation of the infant after delivery.

Women who have type 1, type 2, or type 3 VWD and have FVIII levels <50 IU/dL, VWF:RCo <50 IU/dL, or a history of severe bleeding should be referred for prenatal care and delivery to a center that, in addition to specialists in high-risk obstetrics, has a hemophilia treatment center and/or a hematologist with expertise in hemostasis. Laboratory, pharmacy, and blood bank support is essential. Before any invasive procedure, such as chorionic villus sampling, amniocentesis, or cervical cerclage, women who have VWD should have laboratory assays for FVIII and VWF:RCo in order to receive appropriate prophylaxis.355,356 FVIII and VWF:RCo levels should be obtained in the third trimester of pregnancy to facilitate planning for the delivery.356 Before delivery, all women who have VWD should meet with an anesthesiologist to plan for the possible need for the administration of hemostatic agents, and/or alternatives, if necessary, for regional anesthesia at the time of delivery.355 A pregnant woman carrying a baby at risk for type 3 or severe types 1 or 2 VWD should be referred to a pediatric hematologist to discuss neonatal testing and potential bleeding in the infant.85,354,375

There are limited data on the use of DDAVP for VWD in pregnancy. Mannucci reported using DDAVP for prophylaxis prior to procedures in 31 pregnant women "without mishap,"357 but specific data are not provided. DDAVP, in the lower doses used to treat diabetes insipidus, however, is generally thought to be safe for mother and fetus. In a review of 53 cases of women who were pregnant and used DDAVP, administered in doses of 7.5-100 micrograms a day for diabetes insipidus, no adverse maternal or neonatal effects were attributable to the medication.274 In an in vitro placenta model, DDAVP did not cross the placenta in detectable amounts.274

Tranexamic acid crosses the placenta358 but has been used to treat bleeding during pregnancy in a limited number of cases without adverse fetal effects.359-364 Data regarding aminocaproic acid in pregnancy are limited, but aminocaproic acid was not found to be teratogenic in rabbits.365 In cases of its use during pregnancy, no adverse fetal effects have been reported.366

Miscarriage and Bleeding During Pregnancy

In the general population, miscarriage is common, and 12-13.5 percent of diagnosed pregnancies result in spontaneous abortion.367,368 Although detailed data were not provided, in a study of 182 females who had severe VWD, Lak et al.85 reported that miscarriage was no more frequent than in the general population. Other studies, however, have found a higher incidence of miscarriage among women who have VWD compared to controls145 or compared to the background rate.322,354 Bleeding complications during pregnancy other than miscarriage have been reported.322,323,369-371 Kadir et al.354 found that 33 percent of women who had VWD bled during their first trimester.

Childbirth

Table 17 summarizes nine case series reporting pregnancy outcomes in women who had VWD, including rates of miscarriage, peripartum prophylaxis, postpartum hemorrhage, and perineal hematoma. Prophylaxis included cryoprecipitate, fresh frozen plasma, DDAVP, and factor replacement.

No large prospective studies correlate VWF:RCo and FVIII levels with the risk of bleeding at the time of childbirth, but the opinion of experts is that VWF:RCo and FVIII levels of 50 IU/dL should be achieved before delivery323 and maintained for at least 3-5 days afterward.9,215,323,354-356 There is no consensus on levels of VWF:RCo and FVIII that are safe for regional anesthesia,372 but if VWF:RCo and FVIII levels are ?50 IU/dL and the coagulation screen is normal, regional anesthesia may be considered safe.354

DDAVP may be used to raise factor levels in responders, but care must be taken in its administration at the time of childbirth. Women commonly receive 1-2 liters or more of fluid at the time of a vaginal delivery and 2-3 liters or more at the time of cesarean delivery. Fluids containing oxytocin, which also causes fluid retention, combined with DDAVP may result in fluid retention and life-threatening hyponatremia. Chediak and colleagues reported complications of fluid retention in two women who received DDAVP at the time of childbirth. One woman who received three doses 18 hours apart developed severe hyponatremia (sodium level of 108 mEq/L) and experienced grand mal seizures.371

Table 17. Pregnancies in Women Who Have VWD

Cryo, cryoprecipitate; DDAVP, 1-desamino-8-D-arginine vasopressin (desmopressin, a synthetic analog of vasopressin); FFP, fresh frozen plasma; FVIII, FVIII concentrate; Haemate P®, European equivalent of Humate-P®; NHS 8Y, National Health Services (United Kingdom) factor VIII concentrate (8Y); VWD, von Willebrand disease. 
* Primary, postpartum hemorrhage within the first 24 hours after delivery 
† Secondary, postpartum hemorrhage after 24 hours after delivery

Because NSAIDs, commonly prescribed for pain after childbirth, may decrease platelet function and systemic hemostasis,319 alternative analgesics should be considered.

Postpartum Hemorrhage

Postpartum hemorrhage is an anticipated problem among women who have VWD. By the end of gestation, an estimated 10-20 percent of a woman's blood volume, or at least 750 mL/minute, flows through the uterus.373 After delivery of the infant and placenta, the uterus must contract, and the uterine vasculature must constrict to prevent exsanguination.374 Failure of the uterus to contract is the single most important cause of postpartum hemorrhage.374 Nonetheless, women who have VWD are at an increased risk of postpartum hemorrhage compared to controls.137,145,321 Multiple case series document an increased incidence of postpartum hemorrhage in women who have VWD (see Table 17).

Perineal hematoma, a rare complication of vaginal birth, occurs with some frequency in women who have VWD. Greer et al.323 reported one hematoma in 13 vaginal deliveries, and Kadir and colleagues354 reported three hematomas in 49 vaginal deliveries. This is a relatively high frequency compared to a rate of only 2.2/1,000 in a cohort of 26,187 spontaneous or operative vaginal deliveries.378

In women who have VWD, vaginal bleeding is frequently reported to occur more than 2-3 weeks postpartum. The duration of bleeding after delivery in a normal patient is a median of 21-27 days.379-381 However, the VWF levels that are elevated during pregnancy return to baseline within 7-21 days,382,383 predisposing women who have VWD to delayed postpartum hemorrhage. In the absence of a bleeding disorder, delayed or secondary postpartum hemorrhage is rare and occurs following less than 1 percent of deliveries.384,385 In contrast, 20-25 percent of women who had VWD had delayed postpartum hemorrhage, making delayed postpartum hemorrhage 15-20 times more common among these women compared to normal subjects.354,376

Among the published series of cases of women who were pregnant and had VWD (Table 17), multiple cases of postpartum hemorrhage occurred despite prophylaxis. The average time of presentation of postpartum hemorrhage in women who have VWD was estimated to be 15.7 ± 5.2 days after delivery.386 The implication is that women who have VWD may require frequent evaluation—and possibly prophylaxis—for 2 weeks or more postpartum. Weekly contact with these women is recommended during the postpartum period.356

Management Recommendations

The recommendations are graded according to criteria described in the "Introduction" and in Table 1. Evidence tables are provided for recommendations given a grade of B and having two or more references.

4. Testing Prior to Treatment

• Before treatment, all persons suspected of having VWD should have a laboratory-confirmed diagnosis of type and severity of VWD. This recommendation does not preclude treatment that may be indicated for urgent or emergency situations, despite the absence of confirmatory laboratory data. 
• Grade C, level IV85,136-142
• Persons who do not have a definite diagnosis of VWD but who have VWF:RCo levels of 30-50 IU/dL and have a bleeding phenotype may merit treatment or prophylaxis of bleeding in certain clinical situations. 
• Grade B, level III196
• Persons with >10 IU/dL VWF:RCo and >20 IU/dL FVIII activity levels should undergo a trial of DDAVP while in a nonbleeding state. Persons with levels below these thresholds are less likely to demonstrate clinical or laboratory responses to DDAVP, but a DDAVP trial should still be considered in these individuals. 
• Grade B, level IIa99,223,224,227,231See Evidence Table 6.

5. General Management

• Treatment of persons who have VWD is aimed at cessation of bleeding or prophylaxis for surgical procedures. 
• Grade C, level IV1,7,9
• Continued bleeding, despite adequately replaced VWF:RCo and FVIII activity levels, requires evaluation of the person for other bleeding etiologies, including anatomic. 
• Grade C, level IV
• Long-term prophylaxis is currently under investigation in an international cooperative study, and the long-term risks and benefits should be considered carefully. 
• Grade C, level IV211,212
• Individuals who are more than 2 years of age, who have VWD and have not already been vaccinated, should be immunized against hepatitis A and B. 
• Grade C, level IV299
• Persons who have VWD should have the opportunity to talk to a knowledgeable genetic counselor. 
• Grade C, level IV355
• At diagnosis, persons who have VWD should be counseled to avoid aspirin, other NSAIDs, and other platelet-inhibiting drugs. 
• Grade C, level IV300-302
• Restriction of fluids to maintenance levels should be considered in persons receiving DDAVP (especially for young children and in surgical settings) to avoid the occurrence of hyponatremia and seizures. 
• Grade C, level IV264-266

6. Treatment of Minor Bleeding and Prophylaxis for Minor Surgery

• Epistaxis and oropharyngeal, soft tissue, or minor bleeding should be treated with intravenous or nasal DDAVP, if appropriate, based on trial testing. 
• Grade B, level IIa221-223,230,246See Evidence Table 7
• If elevation of VWF is necessary and response to DDAVP is inadequate, VWF concentrate should be used, with dosing primarily based on VWF:RCo units and secondarily on FVIII units. 
• Grade C, level IV247,253
• For prophylaxis for minor surgery, initial treatment should be expected to achieve VWF:RCo and FVIII activity levels of at least 30 IU/dL and preferably >50 IU/dL. 
• Grade B, level III223,230,242,247See Evidence Table 8
• For minor surgery, VWF:RCo and FVIII activity levels of at least 30 IU/dL and preferably >50 IU/dL should be maintained for 1-5 days. 
• Grade B, level III243,244,247,256See Evidence Table 9.
• For persons who have VWD, management of minor bleeding (e.g., epistaxis, simple dental extraction, or menorrhagia) with DDAVP and proper fluid restriction can be performed without laboratory monitoring unless Stimate® or DDAVP is used more than three times within 72 hours. 
• Grade C, level IV263,320
• For persons who have mild to moderate VWD, antifibrinolytics combined with DDAVP are generally effective for oral surgery. VWF concentrate should be available for persons who cannot receive DDAVP or who bleed excessively despite this combined therapy. 
• Grade B, level IIb221,223,232,242,246-248See Evidence Table 10.
• Topical agents, such as fibrin sealant or bovine thrombin, may be useful adjuncts for oral surgery in persons who have VWD. Careful attention to hemostasis of an extraction socket and to suturing of sockets is also important in oral surgery in persons who have VWD. 
• Grade C, level IV242,297

7. Treatment of Major Bleeding and Prophylaxis for Major Surgery

• All treatment plans should be based on objective laboratory determination of response of VWF:RCo and FVIII activity levels to DDAVP or to VWF concentrate infusion. 
• Grade B, level IIb136,231,240,241,244,245,247,249,251-256,290,291See Evidence Tables 11 and 12.
• Whenever possible, all major surgeries and bleeding events should be treated in hospitals with a 24-hour/day laboratory capability and with clinical monitoring by a team including a hematologist and a surgeon skilled in the management of bleeding disorders. 
• Grade C, level IV
• For severe bleeding (e.g., intracranial, retroperitoneal) or for prophylaxis of major surgery, initial target VWF:RCo and FVIII activity levels should be at least 100 IU/dL. Subsequent dosing should maintain VWF:RCo and FVIII levels above a trough of 50 IU/dL for at least 7-10 days. 
• Grade B, level III244,247,251-256,290,291See Evidence Table 12.
• To decrease risk of perioperative thrombosis, VWF:RCo levels should not exceed 200 IU/dL, and FVIII activity should not exceed 250 IU/dL. 
• Grade C, level IV280-282
• For major surgical procedures in selected patients with type 3 VWD or AVWS who are at risk for poor VWF recovery because of inhibitors, a pre-operative trial infusion of VWF concentrate with pharmacokinetic laboratory monitoring should be considered. 
• Grade C, level IV

8. Management of Menorrhagia and Hemorrhagic Ovarian Cysts in Women Who Have VWD

• Women who have menorrhagia or abnormal vaginal bleeding should have a full gynecological evaluation before therapy. 
• Grade C, level IV316
• In the adolescent or adult woman who does not desire pregnancy, but may desire future childbearing, the first choice of therapy for menorrhagia should be combined oral contraceptives. 
• Grade B, level III322
• In the adolescent or adult woman who does not desire pregnancy, but may desire future childbearing, the first choice of therapy to prevent hemorrhagic ovarian cysts should be combined oral contraceptives. 
• Grade C, level IV349,350,352
• If a woman would otherwise be a suitable candidate for an intrauterine device, the second choice of therapy for menorrhagia should be the levonorgestrel intrauterine system. 
• Grade B, level IIb324
• For the woman who desires pregnancy, DDAVP, antifibrinolytics, or VWF concentrate may be tried to control menorrhagia. 
• Grade C, level IV322
• Dilation and curettage is not usually effective to manage excessive uterine bleeding in women who have VWD. 
• Grade C level IV323,340

9. Management of Pregnancy and Childbirth in Women Who Have VWD

• Women planning for pregnancy should have, before conception, an evaluation with a hematologist and a high-risk obstetrician, both of whom are skilled in the management of VWD. 
• Grade C, level IV355
• Women who have type 1, type 2, or type 3 VWD, with FVIII or VWF:RCo levels <50 IU/dL or a history of severe bleeding:
  • Should be referred to a center that has high-risk obstetrics capabilities and with expertise in hemostasis for prenatal care, delivery, termination of pregnancy, or management of miscarriage. 
  • Grade C, level IV
  • Should receive prophylaxis with DDAVP or VWF concentrate before invasive procedures. 
  • Grade C, level IV355,356
  • Should achieve VWF:RCo and FVIII levels of at least 50 IU/dL before delivery and maintain that level for at least 3-5 days afterward. 
  • Grade C, level IV9,215,323,354,356
• If VWF:RCo and FVIII levels can be monitored and maintained above 50 IU/dL during labor and delivery, and no other coagulation defects are present, then regional anesthesia may be considered. 
• Grade C, level IV354
• Because coagulation factors return to prepregnancy levels within 14-21 days after delivery, health care providers should be in close contact with women during the postpartum period. 
• Grade C, level IV356

10. Acquired von Willebrand Syndrome

• Individuals who have AVWS and who require surgery should be considered for a pharmacokinetic trial of therapy with DDAVP and/or VWF concentrate, with monitoring of VWF:RCo and FVIII levels, to evaluate for possible accelerated clearance of VWF. 
• Grade C, level IV117,157
• For persons who have AVWS and who bleed excessively despite therapy with DDAVP and VWF concentrate, treatment with high-dose IGIV should be considered, especially in IgG isotype MGUS (see "Acquired von Willebrand Syndrome" for discussion of this non-FDA-approved use). 
• Grade B, level IIa117,303-306 See Evidence Table 13.

Many recommendations in this guideline are based on relatively limited evidence, thus underscoring the need for further research. Some of these opportunities are discussed below.

Pathophysiology and Classification of VWD

Determinants of VWF level and bleeding risk. The risk of bleeding in persons who have VWD depends on the level of functional VWF and on many other factors that are poorly understood. The plasma level of VWF can be influenced by mutations within or near the VWF gene. In addition, VWF levels depend on ABO blood type,43 possibly on the Secretor locus,109 and on hormonal status and stress, as discussed in "The VWF Protein and Its Functions In Vivo" section. Relatively few of the genetic and nongenetic determinants of VWF level have been characterized, and how they interact is not known. In addition, little quantitative information is available on the risk of specific bleeding symptoms as a function of the level of VWF in plasma. This information would be particularly useful for the management of patients who have VWF levels in the range of 30—50 IU/dL, for whom the risk of medically significant bleeding is not well defined.

VWF level in plasma alone does not account for the observed variation in bleeding symptoms, and recent studies are starting to uncover some of the underlying reasons. For example, persons who have both low VWF and defects in platelet aggregation have more severe bleeding.387 Increased bleeding also has been associated with specific DNA markers for platelet membrane proteins.388 It is likely that multiple hemostatic risk factors interact with VWF level in plasma to determine the likelihood of bleeding or thrombosis. Understanding these interactions and incorporating them into clinical practice will require additional basic, clinical, and epidemiological research.

Heterogeneity of type 1 VWD. Partial quantitative deficiency of VWF can be caused by several mechanisms, as discussed in the section on "Classification of VWD Subtypes." Some persons have dominant VWF mutations that either decrease the secretion of VWF multimers or accelerate their clearance from the circulation. The prevalence of increased clearance as a cause of type 1 VWD is not known. Whether these different disease mechanisms correlate with distinct clinical features, including response to specific treatments, also is not known. Because type 1 VWD is the most common form of VWD, answers to these questions may have important consequences for medical practice.

Heterogeneity of type 2 VWD. The concentration of hemostatically effective large VWF multimers can be selectively decreased by accelerated proteolysis or by a variety of defects in multimer assembly.49 These variants now are grouped together as type 2A VWD, but further subdivision of this category would be justifiable if specific mechanisms of disease were associated with different clinical symptoms or responses to therapy.

Most persons who have type 2M VWD have been identified by finding a profound defect in ristocetin-induced binding to platelets associated with a normal VWF multimer pattern.55,67,72 Defects in binding to collagen or other connective tissue elements could cause a similar bleeding phenotype, but the VWF:RCo assay is insensitive to such defects.73 Collagen-binding abnormalities can be detected by the VWF:CB assays, but those assays are not used widely in the United States. The prevalence and medical significance of collagen-binding defects in type 2M VWD deserve further study.

Diagnosis and Evaluation

Assessment of bleeding signs and symptoms. The initial evaluation of patients for a medically significant bleeding disorder can be difficult because mild bleeding is very common in the healthy population. Specific symptoms have been assessed for clinical relevance in retrospective studies, and some appear to discriminate among healthy controls and persons who have diagnosed bleeding disorders (Box 1). However, the utility of these questions must be established prospectively for less highly selected persons.

Quality and availability of laboratory testing. Reliable testing for VWF:Ag and FVIII is widely available, but VWF:RCo, RIPA, and VWF multimer analysis are much more variable in their performance characteristics and can be difficult to obtain. Also, tests of VWF—FVIII binding (VWF:FVIIIB) are offered by very few laboratories. More robust methods for assessing VWF function and multimer structure must be developed for routine use in the diagnosis of VWD. In addition, the sensitivity and specificity of test ratios such as VWF:RCo/VWF:Ag should be established for identifying the qualitative defects that characterize type 2A and type 2M VWD. Criteria should be established for VWF multimer analysis to distinguish a significant decrease in large multimers (in types 2A and 2B VWD) from a substantially normal multimer distribution (in types 1, 2M, and 2N VWD).

VWF gene sequencing. Mutations that cause many types of VWD can be identified by sequencing the VWF gene in DNA samples from patients.23 The locations of mutations appear to correlate well with some disease phenotypes, suggesting that DNA sequencing could be a useful diagnostic method in VWD. With appropriate study and experience, DNA sequencing may become economical and feasible for routine use. In addition, the widespread application of VWF gene sequencing would provide invaluable information about the prevalence of VWF mutations as a function of VWF level, the strength of the relationship between VWF genotype and VWD phenotype, the penetrance of specific mutations, and the biochemical mechanisms that cause VWD. This knowledge also would be an outstanding resource for the identification and characterization of other factors that modify bleeding symptoms in VWD.

Management of VWD

Many of the standard treatments for VWD have limited experimental support. For example, the intensity and duration of therapy necessary to control bleeding have not been established for many clinical situations and often have been extrapolated from anecdotal experience in hemophilia. The indications for prophylaxis of bleeding also are not well defined. These issues should be addressed by appropriate clinical studies.

DDAVP. Many persons who have VWD respond to DDAVP with a clinically useful rise in VWF and FVIII, but the likelihood of a good outcome depends on the type of VWD and the underlying biochemical mechanism of disease. In type 1 VWD, persons who have accelerated clearance of plasma VWF may have a transient response to DDAVP.41,232 Whether DDAVP should be used at all in persons who have type 2B VWD is controversial.229,237,257—259,389—391 In type 2N VWD, the baseline FVIII level may be a good predictor of the magnitude and duration of the FVIII response to DDAVP.77,224,228,392 The drug is thought to be safe for use in pregnancy, but the published experience in this setting is limited.273,274 Hyponatremia and thrombotic events have occurred after DDAVP, but risk factors for these events and their incidence have not been established. These important clinical issues should be addressed by studies of DDAVP in specific types of VWD. In addition, the availability of DDAVP for subcutaneous administration may improve management of VWD.

Factor Concentrates. The available plasma—derived products that contain VWF also contain FVIII as part of the FVIII—VWF complex, and only two such products (Humate-P® and Alphanate SD/HT®) are currently licensed in the United States for treatment of VWD. When administered to patients who have VWD, the infused FVIII may add to the endogenous FVIII production and cause markedly elevated FVIII levels that are much greater than the VWF levels achieved with treatment; these have been associated with thrombosis.215 High FVIII levels can be avoided by adjusting the dose of product administered, but VWF levels then may be relatively low. Whether FVIII or VWF levels, or both, should be used to monitor treatment with FVIII—VWF concentrates is unknown. Use of a pure VWF product in place of FVIII—VWF concentrates would avoid the disproportionate increase in FVIII. A pure VWF concentrate has been used in Europe393 but is not currently available in the United States. Studies are needed to establish appropriate treatment and monitoring regimens for these products. In addition, prelicensure studies of recombinant VWF are needed to establish its safety, efficacy, and role in the treatment of VWD. The licensing of other products, containing both VWF and FVIII, also would enhance therapeutic options.

Platelets. Approximately 15 percent of the total VWF in blood is found within platelets, and platelet VWF appears to contribute to hemostasis. Although VWD patients who have abnormal or low platelet VWF have been described, there has been only limited exploration of the feasibility and utility of such testing, in part because of limitations of practical methodologies. Clinically, platelet transfusions have been reported to stop bleeding in some patients who have VWD and were not helped by transfusion of FVIII—VWF concentrates.293,294 The efficacy and appropriate use of platelet transfusions in persons who have VWD or AVWS need to be established.

Antifibrinolytics. Tranexamic acid and aminocaproic acid have been used alone or as adjunctive therapy to treat bleeding in VWD. The safety, efficacy, and optimal dosing of these agents in VWD should be established by suitable clinical studies. In addition, the availability of orally administered tranexamic acid would broaden the therapeutic options for antifibrinolytic therapy.

Gene Therapy of VWD

Severe type 3 VWD potentially can be treated with gene therapy. The gene for VWF is larger than could easily be introduced into many vectors, but "gutless" adenoviral vectors could easily accommodate a gene the size of VWF (8.5 kilobases). The prevalence of type 3 VWD and its clinical symptoms, however, does not place it in a high priority category for gene therapy trials. Point mutation repair initially was an exciting approach for VWD,394,395 but followup studies have not achieved the same rate of success in vitro.396,397

Issues Specific to Women

VWF is particularly important for hemostasis during menses and at childbirth. Consequently, women are affected disproportionately by having VWD, especially during their childbearing years.

Menorrhagia. The incidence of menorrhagia appears to vary inversely with VWF level, independent of whether women meet criteria for having VWD.45 Because menorrhagia is so common, even a small reduction in its severity could have significant implications for women’s health. As discussed in the section on menorrhagia, several treatments have been used for menorrhagia associated with VWD, but their efficacy has not been demonstrated convincingly. Therefore, clinical studies would be useful to establish the effect of VWF level on menorrhagia and to evaluate specific treatments for women who have VWD or low plasma levels of VWF.

Labor and delivery. Several small case series indicate that women who have VWD and VWF levels <50 IU/dL at delivery have an increased incidence of immediate and delayed postpartum hemorrhage. These complications appear to be prevented by replacement therapy with FVIII—VWF concentrate before delivery and by either concentrate or DDAVP in the postpartum period.85,354,377 How the risk of bleeding correlates with VWF level or FVIII level is not known, and the required intensity and duration of therapy have not been established.

Training of Specialists in Hemostasis

In the United States, despite scientific progress in basic and clinical research in bleeding and thrombotic disorders, including VWD, there is a shortage of skilled clinicians and laboratorians with expertise in hemostasis.398 Training opportunities need to be developed and/or expanded for hemostasis specialists. Recent clinical training opportunities include a new NHLBI initiative for training in nonmalignant hematology (RFA HL06-006; information available at: http://grants.nih.gov/grants/guide/rfa-files/RFA-HL-06-006.html) and a recent initiative from the U.S. National Hemophilia Foundation (NHF Clinical Fellowship Program). Recognition of hemostasis as a bona fide clinical and laboratory subspecialty in the United States could enhance entry into the field.

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Evidence Table 1. Recommendation I.B.

If answers to probe questions I.B.1-8 are positive, obtain relevant specific information.

Grade B, level IIb

CDC, Centers for Disease Control and Prevention

Evidence Table 2. Recommendation II.B

Initial tests for diagnosing or excluding VWD include the following three tests: VWF:RCo, VWF:Ag, and FVIII activity.

Grade B, level III

VWF, von Willebrand factor; VWF:Ag, von Willebrand factor antigen; VWF:CB, von Willebrand factor collagen-binding activity; VWF:RCo, von Willebrand factor ristocetin cofactor activity

Evidence Table 3. Recommendation II.C.1.a

The first set of additional tests may include evaluation of ratio of VWF activity (VWF:RCo and/or VWF:CB) to VWF:Ag (only in laboratories that have defined reference ranges for the ratio(s))

Grade B, level III

ELISA, enzyme-linked immunosorbent assay; GPIb, glycoprotein Ib; ISTH, International Society on Thrombosis and Haemostasis; PFA-100®, platelet function analyzer; VWF, von Willebrand factor; VWF:Ac, von Willebrand factor activity; VWF:Ag, von Willebrand factor antigen; VWF:CB, von Willebrand factor collagen-binding activity; VWF:RCo, von Willebrand factor ristocetin cofactor activity

Evidence Table 4. Recommendation II.C.1.d

The first set of additional tests may include VWF collagen binding activity (VWF:CB)

Grade B, level IIb

GPIb, glycoprotein Ib; MAB, monoclonal antibody; VWF:Ag, von Willebrand factor antigen; VWF:CB, von Willebrand factor collagen-binding activity; VWF:RCo, von Willebrand factor ristocetin cofactor activity

Evidence Table 5. Recommendation II.C.2

Studies in selected patients, especially those who have a discordantly low FVIII activity compared to VWF levels and who are suspected of having type 2N VWD, should include a FVIII binding assay (VWF:FVIIIB).

Grade B, level IIb

FVIII, [blood clotting] factor VIII; VWF:Ag, von Willebrand factor antigen; VWF:CB, von Willebrand factor collagen-binding activity; VWF:FVIIIB, von Willebrand factor: factor VIII binding assay; VWF:RCo, von Willebrand factor ristocetain cofactor activity

Evidence Table 6. Recommendation IV.C

Persons with >10 IU/dL VWF:RCo and >20 IU/dL FVIII activity levels should undergo a trial of DDAVP while in a nonbleeding state. Persons with levels below these thresholds are less likely to demonstrate clinical or laboratory responses to DDAVP, but a DDAVP trial should still be considered in these individuals.

Grade B, level IIa

BT, bleeding time; DDAVP, 1-desamino-8-D-arginine vasopressin (desmopressin, a synthetic analog of vasopressin); FVIII, [blood clotting] factor VIII; VWF, von Willebrand factor; VWF:Ag, von Willebrand factor antigen; VWF:RCo, von Willebrand factor ristocetin cofactor activity

Evidence Table 7. Recommendation VI.A

Epistaxis and oropharyngeal, soft tissue, or minor bleeding should be treated with intravenous or nasal DDAVP, if appropriate, based on trial testing.

Grade B, level IIa

BT, bleeding time; DDAVP, 1-desamino-8-D-arginine vasopressin (desmopressin, a synthetic analog of vasopressin); FVIII, [blood clotting] factor VIII; FVIII:C, factor VIII coagulant activity; VWF, von Willebrand factor; VWF:Ag, von Willebrand factor antigen; VWF:RCo, von Willebrand factor ristocetin cofactor activity

Evidence Table 8. Recommendation VI.C

For prophylaxis for minor surgery, initial treatment should be expected to achieve VWF:RCo and FVIII activity levels of at least 30 IU/dL and preferably >50 IU/dL.

Grade B, level III

BT, bleeding time; CFC, clotting factor concentrate; DDAVP, 1-desamino-8-D-arginine vasopressin; FVIII, [blood clotting] factor VIII; VWF:RCo, von Willebrand factor ristocetin cofactor activity

Evidence Table 9. Recommendation VI.D

For minor surgery, VWF:RCo and FVIII activity levels of at least 30 IU/dL and preferably >50 IU/dL should be maintained for 1-5 days

Grade B, level III

CFC, clotting factor concentrate; DDAVP, 1-desamino-8-D-arginine vasopressin; FVIII, [blood clotting] factor VIII; VWF, von Willebrand factor; VWF:Ag, von Willebrand factor antigen; VWF:RCo, von Willebrand factor ristocetin cofactor avtivity

Evidence Table 10. Recommendation VI.F

For persons who have mild to moderate VWD, antifibrinolytics combined with DDAVP are generally effective for oral surgery. VWF concentrate should be available for persons who cannot receive DDAVP or who bleed excessively despite this combined therapy.

Grade B, level IIb

AVWS, acquired von Willebrand syndrome; CFC, clotting factor concentrate; DDAVP, 1-desamino-8-D-arginine vasopressin; EACA, epsilon aminocaproic acid; FVIII, [blood clotting] factor VIII; VWF, von Willebrand factor; VWF:Ag, von Willebrand factor antigen; VWF:RCo, von Willebrand factor ristocetin cofactor activity

Evidence Table 11. Recommendation VII.A

All treatment plans should be based on objective laboratory determination of response of VWF:RCo and FVIII activity levels to DDAVP or to VWF concentrate infusion.

Grade B, level IIb

AVWS, acquired von Willebrand syndrome; DDAVP, 1-desamino-8-D-arginine vasopressin (desmopressin, a synthetic analog of vasopressin); FVIII, [blood clotting] factor VIII; VWF, von Willebrand factor; VWF:RCo, von Willebrand Factor ristocetin cofactor activity

Evidence Table 12. Recommendation VII.C

For severe bleeding (e.g., intracranial, retroperitoneal) or for prophylaxis of major surgery, initial target VWF:RCo and FVIII activity levels should be at least 100 IU/dL. Subsequent dosing should maintain VWF:RCo and FVIII levels above a trough of 50 IU/dL for at least 7-10 days.

Grade B, level III

DDAVP, 1-desamino-8-D-arginine vasopressin; FVIII, [blood clotting] factor VIII; VWF, von Willebrand factor; VWF:Ag, von Willebrand factor antigen; VWF:CB, von Willebrand factor collagen-binding activity; VWF:RCo, von Willebrand factor ristocetin cofactor activity

Evidence Table 13. Recommendation X.B

For persons who have AVWS and who bleed excessively despite therapy with DDAVP and VWF concentrate, treatment with high-dose IGIV should be considered, especially in IgG isotype MGUS (see Treatment of AVWS for discussion of this non-FDA-approved use).

Grade B, level IIa

AVWS, acquired von Willebrand syndrome; DDAVP, 1-desamino-8-D-arginine vasopressin (desmopressin, a synthetic analog of vasopressin); FVIII, [blood clotting] factor VIII; FVIII:C, factor VIII coagulant activity; IgG, immunoglobulin G; IGIV, immune globulin intravenous (also known as IVIG); IgM, immunoglobulin M; ISTH, International Society on Thrombosis and Haemostasis; MGUS, monoclonal gammopathy of uncertain significance; VWF, von Willebrand factor; VWF:Ag, von Willebrand factor antigen; VWF:RCo, von Willebrand factor ristocetin cofactor activity