Deep vein thrombosis (throm-BO-sis), or DVT, is a blood clot that forms in a vein deep in the body. Blood clots occur when blood thickens and clumps together.
Most deep vein blood clots occur in the lower leg or thigh. They also can occur in other parts of the body.
A blood clot in a deep vein can break off and travel through the bloodstream. The loose clot is called an embolus (EM-bo-lus). It can travel to an artery in the lungs and block blood flow. This condition is called pulmonary embolism (PULL-mun-ary EM-bo-lizm), or PE.
PE is a very serious condition. It can damage the lungs and other organs in the body and cause death.
Blood clots in the thighs are more likely to break off and cause PE than blood clots in the lower legs or other parts of the body. Blood clots also can form in veins closer to the skin's surface. However, these clots won't break off and cause PE.
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Blood clots can form in your body's deep veins if:
The risk factors for deep vein thrombosis (DVT) include:
Your risk for DVT increases if you have more than one of the risk factors listed above.
The signs and symptoms of deep vein thrombosis (DVT) might be related to DVT itself or pulmonary embolism (PE). See your doctor right away if you have signs or symptoms of either condition. Both DVT and PE can cause serious, possibly life-threatening problems if not treated.
Only about half of the people who have DVT have signs and symptoms. These signs and symptoms occur in the leg affected by the deep vein clot. They include:
Some people aren't aware of a deep vein clot until they have signs and symptoms of PE. Signs and symptoms of PE include:
Rapid breathing and a fast heart rate also may be signs of PE.
Your doctor will diagnose deep vein thrombosis (DVT) based on your medical history, a physical exam, and test results. He or she will identify your risk factors and rule out other causes of your symptoms.
For some people, DVT might not be diagnosed until after they receive emergency treatment for pulmonary embolism (PE).
To learn about your medical history, your doctor may ask about:
Your doctor will check your legs for signs of DVT, such as swelling or redness. He or she also will check your blood pressure and your heart and lungs.
Your doctor may recommend tests to find out whether you have DVT.
The most common test for diagnosing deep vein blood clots is ultrasound. This test uses sound waves to create pictures of blood flowing through the arteries and veins in the affected leg.
Your doctor also may recommend a D-dimer test or venography (ve-NOG-rah-fee).
A D-dimer test measures a substance in the blood that's released when a blood clot dissolves. If the test shows high levels of the substance, you may have a deep vein blood clot. If your test results are normal and you have few risk factors, DVT isn't likely.
Your doctor may suggest venography if an ultrasound doesn't provide a clear diagnosis. For venography, dye is injected into a vein in the affected leg. The dye makes the vein visible on an x-ray image. The x ray will show whether blood flow is slow in the vein, which may suggest a blood clot.
Other tests used to diagnose DVT include magnetic resonance imaging (MRI) and computed tomography (to-MOG-rah-fee), or CT, scanning. These tests create pictures of your organs and tissues.
You may need blood tests to check whether you have an inherited blood clotting disorder that can cause DVT. This may be the case if you have repeated blood clots that are not related to another cause. Blood clots in an unusual location (such as the liver, kidney, or brain) also may suggest an inherited clotting disorder.
If your doctor thinks that you have PE, he or she may recommend more tests, such as a lung ventilation perfusion scan (VQ scan). A lung VQ scan shows how well oxygen and blood are flowing to all areas of the lungs.
For more information about diagnosing PE, go to the Health Topics Pulmonary Embolism article.
Doctors treat deep vein thrombosis (DVT) with medicines and other devices and therapies. The main goals of treating DVT are to:
Your doctor may prescribe medicines to prevent or treat DVT.
Anticoagulants (AN-te-ko-AG-u-lants) are the most common medicines for treating DVT. They're also known as blood thinners.
These medicines decrease your blood's ability to clot. They also stop existing blood clots from getting bigger. However, blood thinners can't break up blood clots that have already formed. (The body dissolves most blood clots with time.)
Blood thinners can be taken as a pill, an injection under the skin, or through a needle or tube inserted into a vein (called intravenous, or IV, injection).
Warfarin and heparin are two blood thinners used to treat DVT. Warfarin is given in pill form. (Coumadin® is a common brand name for warfarin.) Heparin is given as an injection or through an IV tube. There are different types of heparin. Your doctor will discuss the options with you.
Your doctor may treat you with both heparin and warfarin at the same time. Heparin acts quickly. Warfarin takes 2 to 3 days before it starts to work. Once the warfarin starts to work, the heparin is stopped.
Pregnant women usually are treated with just heparin because warfarin is dangerous during pregnancy.
Treatment for DVT using blood thinners usually lasts for 6 months. The following situations may change the length of treatment:
The most common side effect of blood thinners is bleeding. Bleeding can happen if the medicine thins your blood too much. This side effect can be life threatening.
Sometimes the bleeding is internal (inside your body). People treated with blood thinners usually have regular blood tests to measure their blood's ability to clot. These tests are called PT and PTT tests.
These tests also help your doctor make sure you're taking the right amount of medicine. Call your doctor right away if you have easy bruising or bleeding. These may be signs that your medicines have thinned your blood too much.
These medicines interfere with the blood clotting process. They're used to treat blood clots in patients who can't take heparin.
Doctors prescribe these medicines to quickly dissolve large blood clots that cause severe symptoms. Because thrombolytics can cause sudden bleeding, they're used only in life-threatening situations.
If you can't take blood thinners or they're not working well, your doctor may recommend a vena cava filter.
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 doesn't stop new blood clots from forming.
Graduated compression stockings can reduce leg swelling caused by a blood clot. These stockings are worn on the legs from the arch of the foot to just above or below the knee.
Compression stockings are tight at the ankle and become looser as they go up the leg. This creates gentle pressure up the leg. The pressure keeps blood from pooling and clotting.
There are three types of compression stockings. One type is support pantyhose, which offer the least amount of pressure.
The second type is over-the-counter compression hose. These stockings give a little more pressure than support pantyhose. Over-the-counter compression hose are sold in medical supply stores and pharmacies.
Prescription-strength compression hose offer the greatest amount of pressure. They also are sold in medical supply stores and pharmacies. However, a specially trained person needs to fit you for these stockings.
Talk with your doctor about how long you should wear compression stockings.
You can take steps to prevent deep vein thrombosis (DVT) and pulmonary embolism (PE). If you're at risk for these conditions:
If you've had DVT or PE before, you can help prevent future blood clots. Follow the steps above and:
Contact your doctor at once if you have any signs or symptoms of DVT or PE. For more information, go to "What Are the Signs and Symptoms of Deep Vein Thrombosis?"
The risk of developing DVT while traveling is low. The risk increases if the travel time is longer than 4 hours or you have other DVT risk factors.
During long trips, it may help to:
If you have risk factors for DVT, your doctor may advise you to wear compression stockings while traveling. Or, he or she may suggest that you take a blood-thinning medicine before traveling.
If you've had a deep vein blood clot, you're at greater risk for another one. During treatment and after:
DVT often is treated with blood-thinning medicines. These medicines can thin your blood too much and cause bleeding (sometimes inside the body). This side effect can be life threatening.
Bleeding can occur in the digestive system or the brain. Signs and symptoms of bleeding in the digestive system include:
Signs and symptoms of bleeding in the brain include:
If you have any of these signs or symptoms, seek medical care right away. If you have a lot of bleeding after a fall or injury, call 9–1–1. This could be a sign that your DVT medicines have thinned your blood too much.
You might want to wear a medical ID bracelet or necklace that states you're at risk of bleeding. If you're injured, the ID will alert medical personnel of your condition.
Talk with your doctor before taking any medicines other than your DVT medicines. This includes over-the-counter medicines. Aspirin, for example, also can thin your blood. Taking two medicines that thin your blood may raise your risk of bleeding.
Ask your doctor about how your diet affects these medicines. Foods that contain vitamin K can change how warfarin (a blood-thinning medicine) works. Vitamin K is found in green, leafy vegetables and some oils, like canola and soybean oils. Your doctor can help you plan a balanced and healthy diet.
Discuss with your doctor whether drinking alcohol will interfere with your medicines. Your doctor can tell you what amount of alcohol is safe for you.
The National Heart, Lung, and Blood Institute (NHLBI) is strongly committed to supporting research aimed at preventing and treating heart, lung, and blood diseases and conditions and sleep disorders.
Researchers have learned a lot about blood disorders over the years. That knowledge has led to advances in medical knowledge and care. However, many questions remain about various blood disorders, including deep vein thrombosis (DVT).
The NHLBI continues to support research aimed at learning more about DVT. For example, NHLBI-supported research includes studies that:
Much of the NHLBI's research depends on the willingness of volunteers to take part in clinical trials. Clinical trials test new ways to prevent, diagnose, or treat various diseases and conditions.
For example, new treatments for a disease or condition (such as medicines, medical devices, surgeries, or procedures) are tested in volunteers who have the illness. Testing shows whether a treatment is safe and effective in humans before it is made available for widespread use.
By taking part in a clinical trial, you can gain access to new treatments before they're widely available. You also will have the support of a team of health care providers, who will likely monitor your health closely. Even if you don't directly benefit from the results of a clinical trial, the information gathered can help others and add to scientific knowledge.
If you volunteer for a clinical trial, the research will be explained to you in detail. You'll learn about treatments and tests you may receive, and the benefits and risks they may pose. You'll also be given a chance to ask questions about the research. This process is called informed consent.
If you agree to take part in the trial, you'll be asked to sign an informed consent form. This form is not a contract. You have the right to withdraw from a study at any time, for any reason. Also, you have the right to learn about new risks or findings that emerge during the trial.
For more information about clinical trials related to deep vein thrombosis, talk with your doctor. You also can visit the following Web sites to learn more about clinical research and to search for clinical trials:
For more information about clinical trials for children, visit the NHLBI's Children and Clinical Studies Web page.
The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.