Venous Thromboembolism

Also known as Blood Clots, Deep Vein Thrombosis (DVT), Pulmonary Embolism (PE)
Venous thromboembolism (VTE) is a disorder that includes deep vein thrombosis and pulmonary embolism. A deep vein thrombosis (DVT) occurs when a blood clot forms in a deep vein, usually in the lower leg, thigh, or pelvis. A pulmonary embolism (PE) occurs when a clot breaks loose and travels through the bloodstream to the lungs.

The risk of developing VTE is highest after major surgery or a major injury, or when you have heart failure, cancer, or a heart attack. Swelling, redness, and pain are some of the signs and symptoms of deep vein thrombosis. A pulmonary embolism can cause sudden chest pain and shortness of breath. Sometimes VTE occurs without any obvious signs. Medicines that help prevent further blood clots from forming or that dissolve serious vein blockages are the main treatments for VTE. Without treatment, VTE can restrict or block blood flow and oxygen, which can damage the body’s tissue or organs. This can be especially serious in the case of a pulmonary embolism, which blocks blood flow to the lungs. If a blood clot is large or there are many clots, a pulmonary embolism can cause death.

Explore this Health Topic to learn more about VTE, including deep vein thromboses and pulmonary embolisms; NHLBI’s role in research and clinical trials to improve health; and where to find more information.

Causes

VTE occurs in the veins that carry blood to your heart. A deep vein thrombosis may occur if the flow of blood slows down in your body’s deep veins, if something damages the blood vessel lining, or if the makeup of the blood itself changes so that blood clots form more easily. A pulmonary embolism (PE) refers to an embolus from a deep vein blood clot that breaks loose and travels to the lungs, blocking an artery in the lung. Blood clots can develop in veins damaged by surgery or trauma, or a result of inflammation in response to an infection or injury.

Learn more about how blood clots form.

Risk Factors

Risk factors for VTE include a history of a previous VTE event; surgery; medical conditions such as cancer or spinal cord injury; pregnancy; paralysis or long periods of immobilization; specific genes; and certain circumstances related to age, race, and sex. In most cases of VTE, there is more than one risk factor involved. The more risk factors you have, the greater the chance you have of developing VTE.

Read Life After for information about the risk of repeat VTE events.

Surgery

Knee and hip replacement surgery, in particular, carry a high risk for VTE, as does peripheral and coronary artery bypass surgery, surgery to remove cancer, neurosurgery, abdominal surgery, and other major operations. Clotting is one of the body’s natural ways to heal the damage to your blood vessels from surgery. While you wear a cast or stay in bed to heal, your venous circulation slows because you stop moving as much as usual. This lack of movement increases the risk of blood clotting.

The risk of developing VTE is highest in the first three months after surgery and decreases with time. Ask your medical team about prevention strategies if you are scheduled for major surgery.

Other medical conditions

Certain medical conditions can increase your risk of developing a DVT. Some conditions are more closely linked to getting a DVT than others and include the following:

  • Spinal cord injury. In addition to damaging veins deep in your body, spinal cord injury may cause paralysis, which can reduce blood flow and raise your risk of VTE. The risk is highest in the first weeks after the injury.
  • A broken hip or leg bone or other trauma.
  • Cancers such as advanced brain, breast, colon, and pancreatic cancer. Cancer chemotherapy, surgical treatment, and placement of a central venous catheter—a tube inserted into a vein to deliver chemotherapy treatment or other medicine—all increase the risk of VTE. Some cancers release substances that can make it easier for blood to clot. Some cancerous tumors may directly block blood flow by pressing on a vein. A central venous catheter increases the risk for VTE in arm veins, especially in children.
  • Heart conditions such as heart attack or congestive heart failure.
  • Stroke
  • Obesity
  • Varicose veins. Most varicose veins do not cause problems, but large, untreated varicose veins can lead to VTE.
  • Infections
  • Sickle cell disease. This condition makes the blood clot more easily and can be a risk factor for VTE.

Hormone-based medicines

Women who take birth control pills or get hormone therapy have an increased risk of clotting. Some medicines appear to put people at a higher risk than other medicines do, and the risk tends to be highest in the first few months after starting to take them. If you have other risk factors in addition to taking hormone-based medicines, keep in mind that risk for blood clots may be even higher.

Pregnancy and giving birth

Women are at higher risk for VTE during the first six weeks after giving birth to a baby. The risk is also somewhat higher than usual during pregnancy. This may be due to hormones or other factors in the blood, changes in the way blood flows through your veins, or damage to your blood vessels during delivery. If you are required to be on bed rest while you are pregnant, the lack of movement can reduce blood flow through your veins. Surgery for a cesarean delivery may also increase your risk.

Not moving for long periods

Being still slows blood flow through the veins in your arms and legs, raising your risk of deep vein thrombosis. Especially when combined with other risk factors, not moving for long periods of time—such as when on bed rest in a nursing home or hospital setting, when you have a cast, or during a long flight—can increase your risk. Slower blood flow can create a low-oxygen environment that makes it easier for clots to form or trap blood in places such as the veins in the legs where they have a tougher time breaking up.

Age

VTE can occur at any age, but your risk increases as you age. After age 40, the risk of VTE almost doubles every 10 years.

Family history and genetics

Heredity can affect your chances of developing VTE. Researchers have found dozens of genetic changes that can increase your risk of VTE. Some changes make your blood more likely to clot. If your parents have these genetic changes, you may have inherited them. Studies show that the risk of VTE among siblings of someone who has had VTE is more than double the risk among the general population.

Factor V Leiden is the most common known genetic risk factor for VTE. What is Factor V Leiden?

Race or ethnicity

Studies suggest that the frequency and severity of VTE may vary by a person’s race and ethnicity. In the United States, African Americans have the highest rates of VTE. VTE is less common among Asian Americans and Pacific Islanders. Recent findings have revealed new genetic factors influencing a person’s risk for VTE, and those appear to be more common among African Americans.

Sex

Women in their childbearing years are more likely to develop VTE than men of the same age. After menopause, women’s risk is lower than men’s.

Screening and Prevention

There are no methods to screen for VTE. If you have certain risk factors, such as recent surgery or a major injury, your doctor may start one or more approaches to help prevent a first VTE event.

Prevent a first VTE event

If you are preparing to go to the hospital for a procedure or have other risk factors for VTE, talk with your doctor about a plan for preventing blood clots from forming. Doctors may suggest three ways to help prevent VTE:

  • Movement. Helping your blood circulate makes it harder for clots to form. Your doctor may recommend that you move around as soon as possible after surgery and as you heal. If you cannot get up and walk, try to flex and stretch your feet to improve blood flow in your calves.
  • Pressure. Gentle pressure keeps blood from pooling and clotting. Your doctor may recommend applying pressure—for example, by wearing a sleeve or boot that periodically fills with air, or by wearing graduated compression stockings.
  • Medicines. Your doctor may give you anticoagulant, or blood-thinning, medicines to prevent clotting. Sometimes this preventive therapy starts before surgery. Or, you may be asked to take a blood thinner during your recovery period at home. These medicines, such as heparin, warfarin, and direct oral anticoagulants, are also used to treat VTE.

Your doctor may recommend some combination of these preventive treatments for a month or more after surgery. These approaches to prevention may also be appropriate if you are admitted to the hospital for reasons other than surgery, cannot move for an extended period, or have a condition that makes it more likely that your blood will clot.

Look for

  • Diagnosis will discuss tests and procedures that your doctor may use to diagnose VTE.
  • Life After will explain what your doctor may recommend to prevent your VTE from recurring, getting worse, or causing complications.
  • Research for Your Health will discuss how we are using current research and advancing research to prevent VTE.
  • Participate in NHLBI Clinical Trials will explain our ongoing clinical studies that are investigating prevention strategies for VTE.

Signs, Symptoms, and Complications

The signs and symptoms of VTE are not the same for everyone. Sometimes VTE does not cause symptoms until serious complications occur. In other cases, deep vein thrombosis causes swelling or discomfort near the blood clot. Pulmonary embolism can cause chest pain and difficulty breathing. Pulmonary embolism can be a life-threatening condition.

Signs and symptoms

Deep vein thrombosis may cause the following to occur around the area of a blood clot:

  • Swelling
  • Pain or tenderness
  • Increased warmth, cramps, or aching in the area that is swollen or painful, usually the calf or thigh
  • Red or discolored skin

Signs and symptoms of pulmonary embolism include:

  • Shortness of breath
  • Pain with deep breathing
  • Rapid breathing
  • Increased heart rate

Less common signs and symptoms of pulmonary embolism may include coughing, with or without blood; feelings of anxiety or dread; light-headedness or fainting; and sweating.

Contact your doctor right away if you suspect that you have signs or symptoms of VTE. Deep vein thrombosis should be taken seriously, as it may lead to pulmonary embolism.

Complications

Possible complications of VTE include:

  • Post-thrombotic syndrome (PTS), in which poor blood flow, inflammation, and blood vessel damage from deep vein thrombosis cause swelling and discomfort. PTS is a long-lasting condition that can be disabling. With PTS, you may notice swelling, pain, itchiness, or discoloration in the affected area, along with cramping or fatigue. The symptoms may feel worse if you have been on your feet for an extended period. In severe cases, skin sores may develop. Compression stockings may help relieve PTS symptoms.
  • Pulmonary hypertension, which occurs when pulmonary embolism blocks blood flow and raises blood pressure in the vessels leading to your lungs. This condition can lead to heart failure. If you develop pulmonary hypertension, you may find it hard to breathe, especially after physical activity, or you may cough up blood, notice swelling, feel tired, have palpitations, or faint. If you still have pulmonary hypertension several months after a VTE event, your doctor may refer you to a specialist to talk about the possibility of surgery to remove a lung clot that has not gone away with treatment.

Look for

  • Diagnosis will discuss tests and procedures used to detect signs of blood clots and blockage and help rule out other conditions that may mimic VTE.
  • Treatment will explain treatment-related complications or side effects of VTE, such as bleeding.

Diagnosis

Your doctor will diagnose deep vein thrombosis with or without pulmonary embolism based on your medical history, a physical exam, and various imaging or blood test results. Your doctor will identify your risk factors and rule out other causes of your symptoms.

Medical history and physical exam

Your doctor will ask you about your risk factors and your signs and symptoms for VTE. Your doctor may examine your heart rate and the area that is affected and ask about your overall health, including:

  • Your recent medical history, especially any paralysis or periods of immobilization
  • Medicines you are taking
  • Recent surgeries or injuries you have had
  • Whether you have been treated for cancer

Diagnostic tests and procedures

  • D-dimer test to measure a substance in the blood that is released when the fibrin proteins in a blood clot dissolve. If the test shows high levels of the substance, you may have VTE. If your test results are normal and you have few risk factors, you likely do not have VTE.
  • Ultrasound to look for deep vein blood clots. This test uses sound waves to create pictures of blood flowing in your veins. The person doing the test may press on your veins to see if they compress normally or if they are stiff with blood clots.
  • Computed tomography (CT) angiography to take pictures of your blood vessels and look for blood clots in the lungs and legs. This is the most common diagnostic test for pulmonary embolism.
  • Pulmonary angiography to confirm a pulmonary embolism if, after other testing, your doctor suspects you might have one. This test requires inserting a tube into your blood vessel. It also uses X-rays to create video of the blood flow to your lung so your doctor can identify any blood clots.
  • Other imaging tests to look at blood flow through your veins, heart function, and lung function if the results of previous tests could not diagnose or rule out VTE. These include venography, echocardiography, ventilation/perfusion scanning, and magnetic resonance imaging (MRI).

Tests for other medical conditions

To help diagnose VTE, your doctor may need to do tests to find out if other medical conditions are causing your symptoms. Other tests include:

  • Blood tests to check whether you have an inherited blood clotting disorder if you have had repeated blood clots that are not related to another cause. Blood clots in an unusual location, such as the liver, kidney, or brain, may also suggest an inherited clotting disorder. Blood tests can also measure the level of oxygen and other gases in your blood.
  • Chest X-ray to give your doctor information about what may be causing your symptoms, such as pneumonia or fluid in the lungs. A chest X-ray does not show whether you have a pulmonary embolism.
  • Electrocardiogram (ECG) to identify other conditions that are causing signs of pulmonary embolism. An ECG records the electrical activity of your heart.

Reminders

Treatment

Not everyone who is diagnosed with VTE needs treatment. In some cases, your doctor will detect a clot and decide to monitor it instead of treating it right away. Doctors usually recommend medicines to treat VTE, but a vena cava filter may be used if you cannot take the medicine.

Medicines

Anticoagulants, or blood thinners, and thrombolytics are medicines commonly used to treat VTE.

  • Anticoagulants, or blood thinners, keep blood clots from getting larger and stop new clots from forming. Conventional blood thinners include warfarin and heparin, but newer blood-thinning medicines are also available. To take them, you might get an injection, take a pill, or have an IV tube inserted. Possible side effects include bleeding, especially if you are taking other medicines that also thin your blood, such as aspirin.
  • Thrombin inhibitors interfere with the process of clot formation. They may be used for people who cannot take heparin.
  • Thrombolytics may be used to dissolve large blood clots that cause severe symptoms or other serious complications. Because thrombolytics can cause sudden bleeding, they are used only for serious and potentially life-threatening VTE events, such as pulmonary embolism.

Catheter-assisted thrombus removal

In some cases, including emergencies, a doctor may need to do a catheter-assisted thrombus removal. This procedure uses a flexible tube to reach a blood clot in your lung. The doctor can insert a tool in the tube to break up the clot or to deliver medicine through the tube. Usually you will get medicine to put you to sleep for this procedure.

Vena cava filter

Some people who cannot take blood thinners may need a vena cava filter to treat their deep vein thrombosis. The filter is inserted inside a large vein called the vena cava. The filter catches blood clots before they travel to the lungs, which prevents pulmonary embolism. However, the filter does not stop new blood clots from forming. A filter is not usually recommended if you have taken blood thinners.

Look for

  • Life After will discuss what your doctor may recommend, including lifelong lifestyle changes and medical care to prevent your condition from recurring, getting worse, or causing complications.
  • Research for Your Health will explain how we are using current research and advancing research to treat people who have VTE.
  • Participate in NHLBI Clinical Trials features ongoing clinical studies that are investigating treatments for VTE.

Life After

As you recover from your short-term treatment for VTE, you will need to follow up with your doctor regularly to monitor your condition and discuss whether you need to continue taking blood-thinning medicines. You will also want to take steps to prevent a repeat VTE event and be aware of possible long-term complications. See a doctor or go to the emergency room if you have any signs of excessive bleeding, which can happen if your medicine dose is too high.

Receive routine follow-up care

Follow your doctor’s instructions and schedule regular appointments.

  • Tell your doctor if symptoms such as pain or swelling continue. Your doctor may prescribe graduated compression stockings to give you relief.
  • Take all medicines as prescribed. You will probably keep taking medicines to treat VTE for three months or longer. The most common side effect of blood thinners is bleeding. This side effect can be life-threatening.
  • Check your legs for any signs or symptoms of deep vein clotting, such as swollen areas, pain or tenderness, increased warmth in swollen or painful areas, or red or discolored skin. If you think you may have another deep vein clot or are having symptoms of pulmonary embolism, contact your doctor right away.
  • Tell your doctor if you notice that you bruise easily; have unexpected bleeding, such as when you floss or go to the toilet; or have unusually heavy menstrual periods.

Monitor your condition

To monitor your condition, your doctor may recommend the following tests:

  • Blood tests to monitor the proper dose of medicine so that adjustments can be made as necessary. If you are taking warfarin to treat VTE, you will need to take regular tests that show how long it takes for your blood to clot. Usually, you do these tests at the doctor’s office or at a clinic. The FDA has approved several devices for self-testing. Your doctor may also run regular blood tests to check your kidneys or liver if you have been taking other blood-thinning medicines for more than a year. This will help your doctor make sure your body can still tolerate the medicine well.
  • Ultrasounds to monitor your blood clot. These tests will help your doctor see if your blood clot has gotten bigger or has moved.

Healthy lifestyle changes

When you return home, your doctor may recommend healthy lifestyle changes to help improve your recovery.

  • Heart-healthy eating. Heart-healthy eating includes limiting the amount of alcohol you drink. Alcohol can also be dangerous if you are taking blood-thinning medicine. If you are taking warfarin, talk with your doctor about your eating patterns and any supplements you take. Foods that contain vitamin K can affect how well warfarin works, so it is important to eat about the same amount of vitamin K each day. Vitamin K is found in green leafy vegetables and some oils, such as canola and soybean oils.
  • Being physically active. It is important to keep moving regularly while you are healing. Ask your medical care team when you can start being physically active and how much activity is appropriate.
  • Aiming for a healthy weight. If you are overweight or have obesity, you can improve your health by aiming for a healthy weight. Obesity is a risk factor for a repeat VTE event.
  • Managing stress. Stress can increase the risk of other conditions that can lead to VTE, such as heart attack and stroke.
  • Quitting smoking. Smoking also increases the risk of heart attack and stroke, and it may aggravate other factors known to raise the risk of VTE. Visit Smoking and Your Heart and the National Heart, Lung, and Blood Institute’s Your Guide to a Healthy Heart. For free help quitting smoking, you may call the National Cancer Institute’s Smoking Quitline at 1-877-44U-QUIT (1-877-448-7848).

Prevent a repeat VTE event

Nearly one in three patients who have had VTE will experience a repeat VTE event in the next 10 years. It can take a year or more for clots to break up or stabilize and for blood flow to return to normal. If you were previously treated with blood thinners and experience a repeat VTE event, your doctor may recommend changing your medicine dose or switching you to a different type of blood thinner.

To prevent a repeat VTE event:

  • See your doctor for regular checkups and follow-up tests and treatment.
  • Talk to your doctor about your risk for a repeat VTE event. The risk of a repeat VTE is higher for African Americans and Hispanic Americans than it is for white Americans. It is also higher for men than for women.
  • Take all medicines as your doctor prescribes. A repeat event while you are taking medicines is rare, but if it does occur, your doctor may switch your medicine or increase the dose.
  • If you stop taking blood-thinning medicines, your doctor may suggest that you take aspirin to reduce the risk of getting another clot.

Learn the warning signs of serious complications and have a plan

Medicines used to treat VTE can thin your blood too much or impair your body’s ability to clot after a wound. If you take a dose of blood-thinning medicine that is too high, it may cause bleeding in the digestive system or in the brain. These side effects can be life threatening.

Signs and symptoms of bleeding in the digestive system include:

  • Bright red vomit or vomit that looks like coffee grounds
  • Bright red blood in your stool or black, tarry stools
  • Pain in your abdomen

Signs and symptoms of bleeding in the brain include:

  • Severe pain in your head
  • Sudden changes in your vision
  • Sudden inability to move your legs or arms
  • Memory loss or confusion

A lot of bleeding after a fall or injury, or easy bruising or bleeding, may mean that your blood is too thin. Excessive bleeding is bleeding that will not stop after you apply pressure to a wound for 10 minutes. Call your doctor right away if you have any of these signs. If you have severe bleeding, call 9-1-1.

Research for Your Health

The NHLBI is part of the U.S. Department of Health and Human Services’ National Institutes of Health (NIH)—the Nation’s biomedical research agency that makes important scientific discovery to improve health and save lives. We are committed to advancing science and translating discoveries into clinical practice to promote the prevention and treatment of heart, lung, blood, and sleep disorders, including VTE. Learn about current and future NHLBI efforts to improve health through research and scientific discovery.

Improving health with current research

Learn about the following ways the NHLBI continues to translate current research into improved health for people who have VTE. Research on this topic is part of the NHLBI’s broader commitment to advancing scientific discoveries in blood disorders and blood safety.

  • Surgeon General’s Call to Action to Prevent Deep Vein Thrombosis and Pulmonary Embolism. With the Surgeon General’s office, the NHLBI drafted a call to action summarizing research on VTE and focusing the attention of stakeholders and the public on the importance of saving lives and reducing the burden of VTE.
  • Advances in VTE diagnosis. Clinical trials led by the NHLBI have led to important advances in clinical care. The Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study, originally launched in the 1980s, has tested the accuracy of several technologies used to diagnose pulmonary embolism. Based on the findings of the second phase of this study, investigators issued recommendations. PIOPED research continues, with the aim of finding safer and less expensive approaches to reliably assess patients.
  • Enhancing the translation of research discoveries into improved prevention and treatment of VTE. The NHLBI funds cooperative agreements for research centers to participate in the Translational Research Centers in Thrombotic and Hemostatic Disorders (TRC-THD) program. The individual centers address important clinical questions through research and collaboration with other centers to improve diagnostic tools and treatments for patients who have VTE.
  • Enabling progress in thrombosis research and clinical care through trans-NHLBI and trans-NIH working groups. We regularly convene working groups of experts to discuss where there are gaps in our understanding of VTE. The NHLBI helps identify areas where doctors need more evidence to help make decisions about patients in their care and funds studies to help find the answers. We have organized research meetings around thrombosis in people who have congenital heart disease or cancer, as well as meetings on pulmonary embolism complications such as pulmonary hypertension, how to tailor antithrombotic treatments, and the risk of clotting with heart pumps known as ventricular assist devices.

Learn about some of the pioneering research contributions we have made over the years that have improved clinical care.

Advancing research for improved health

In support of our mission, we are committed to advancing VTE research in the following ways.

  • We perform research. Our Division of Intramural Research includes some of the investigators at NHLBI who are actively engaged in research on VTE.
  • We fund research. Our Division of Blood Diseases and Resources (DBDR) and Division of Lung Diseases (DLD) fund research on VTE. DBDR-supported research improves our understanding of normal and abnormal blood, blood clotting, and blood flow. It also supports scientific advances in biomarkers to diagnose blood conditions and in therapeutics to treat them. The DLD funds research on the causes, diagnosis, prevention, and treatment of lung diseases. Its Lung Vascular Biology Program supports research on pulmonary embolism, including understanding how the condition develops. Search the NIH RePORTer to learn about research the NHLBI is funding on VTE.
  • We stimulate high-impact research. Our Trans-Omics for Precision Medicine (TOPMed) program includes participants with pulmonary embolism and deep vein thrombosis, which may help us understand how genes contribute to differences in disease severity and how patients respond to treatment. The NHLBI Strategic Vision highlights ways we may support research over the next decade.

Learn about exciting research areas the NHLBI is exploring about VTE.

Participate in NHLBI Clinical Trials

We lead or sponsor many studies on venous thromboembolism, including deep vein thrombosis and pulmonary embolism. See if you or someone you know is eligible to participate in our clinical trials.

Do you know someone being treated for cancer who may be at risk for VTE?

This study will assess a medicine called isoquercetin to see if it can prevent a venous thromboembolism (VTE) in patients getting treatment for pancreatic, colorectal, and non-small cell lung cancer. To participate in this study, you must be at least 18 years old and must not have been diagnosed with VTE in the last two years. The study has nine locations in California, Connecticut, Maine, Massachusetts, Missouri, Vermont, and Washington, D.C.

Were you or your child recently diagnosed with VTE?

This study is testing a six-week course of blood-thinning medicines for the treatment of venous thromboembolisms (VTE) to see if they are as effective as the standard treatment course of three months. To participate in this study, you or your child must be younger than 21 years old. This study has 54 locations in Alabama, Arizona, California, Connecticut, Florida, Georgia, Illinois, Indiana, Kentucky, Maryland, Massachusetts, Michigan, Missouri, New Jersey, New York, North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania, South Carolina, Texas, Utah, Virginia, Wisconsin, Australia, Austria, Canada, Israel, and the Netherlands.

Have you or your child been diagnosed with DVT?

This study is comparing two treatments for blockages in veins of the thigh or back: a medicine delivered directly to the blood clot via a tube and standard blood-thinning medicine. The researchers will compare how well both treatments work to resolve the deep vein thrombosis (DVT) in the short term and whether long-term outcomes differ at two years after the initial treatments. To participate in this study, you must be 6 to 21 years old. This study is located in Denver, Colorado.

Was your child recently diagnosed with DVT?

This study will investigate physical activity habits among children recovering from a deep vein thrombosis (DVT) to see if a fitness tracker can help them maintain regular physical activity. The study will also assess the impact of exercise on their health and quality of life. To participate in this study, your child must be between 7 to 21 years old. The study is located in Dallas, Texas.

Do you know a child or young adult recently treated for VTE?

This study is exploring why some people experience complications after venous thromboembolism (VTE) treatment and why others do not. Someday this may help doctors predict which children or young adults are likely to develop complications. To participate in this study, you must have been recently treated for VTE and be younger than 21 years old. This study is located in Dallas, Texas.
More Information

After reading our VTE Health Topic, you may be interested in additional information found in the following resources.