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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 (see Evidence Tables).

Table 1. Level of Evidence

Level Type of Evidence
Ia Evidence obtained from meta-analysis of randomized-controlled trials
Ib Evidence obtained from at least one randomized-controlled trial
IIa Evidence obtained from at least one well-designed controlled study without randomization
IIb Evidence obtained from at least one other type of well-designed quasi-experimental study
III Evidence obtained from well-designed non-experimental descriptive studies, such as comparative studies, correlation studies, and case-control studies
IV Evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities

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.

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