Deep Vein Thrombosis (Blood Clot in the Leg, DVT)

Deep vein thrombosis (DVT) is a blood clot in one of the major deep veins, usually of the lower legs, thighs, or pelvis. A clot blocks blood circulation through these veins, which carries blood from the lower body back to the heart. The blockage can cause pain, swelling, or warmth in the leg. Blood clots in the veins can cause inflammation called thrombophlebitis. If the clot breaks loose and travels through the bloodstream, it can block a blood vessel in the lungs. Called pulmonary embolism, this can lead to severe trouble breathing and even death.

In the U.S., between 300,000 and 600,000 people per year get deep vein thrombosis. About 100,000 people die each year from pulmonary embolism.

Deep Vein Thrombosis Causes

Three things can cause a clot to form inside a blood vessel:

  1. Damage to the inside of a blood vessel
  2. Changes in normal blood flow
  3. Hypercoagulability, a state in which the blood is more likely than usual to clot

Anything that contributes to one or more of these three things can cause deep vein thrombosis. The common risk factors are:

  • Sitting for a long time, such as during a long plane or car ride
  • Long bed rest or immobility, such as after an injury or while ill (for instance, after a stroke)
  • Recent surgery, particularly orthopedic, gynecologic, or heart surgery
  • Recent injury to the lower body, such as fractures of the bones of the hip, thigh, or lower leg
  • Obesity
  • Heart attack or heart failure
  • Recent childbirth
  • Being at very high altitude, greater than 14,000 feet
  • Estrogen replacement therapy or birth control pills
  • Cancer
  • Rare, inherited blood-clotting problems
  • Disseminated intravascular coagulation (DIC), a condition in which blood clotting occurs inappropriately, usually caused by overwhelming infection or organ failure
  • Certain heart or respiratory conditions
  • Advanced age

If a person has one deep vein thrombosis, they are more likely to have a second deep vein thrombosis.

Deep Vein Thrombosis Symptoms


When to Seek Medical Care

Call a doctor immediately if you think you have DVT. Although a deep vein thrombosis may get better on its own, it could also lead to a life-threatening pulmonary embolism. The doctor may tell you to go immediately to a hospital emergency room.

If someone has leg pain or swelling with any risk factors for DVT, go to an emergency room immediately.

Call 911 if you or someone you know begins having chest pain, shortness of breath, difficulty breathing, fainting, or any other symptoms that concern you.

Exams and Tests for Deep Vein Thrombosis

After a physical exam, the doctor might do some of these tests:

  • D-dimer: This blood test measures a substance that is released as a blood clot dissolves. If this blood test is negative, and you have no risk factors for DVT, then it is unlikely that you have a blood clot.
  • Doppler ultrasound: This test uses high-frequency sound waves to show the large veins in the leg and any blood clots. Painless and without complications, this is the most commonly used test to diagnose DVT. But sometimes the test can miss a clot, especially in the smaller veins.
  • Venography: A liquid dye is injected into the veins. It highlights blockage of blood flow by a clot on an image of the legs. This is the most accurate test, but also the most uncomfortable and invasive. It is rarely done today because of the availability of better ultrasound machines.
  • CT scan: This is a type of X-ray that gives a very detailed look at the leg veins in cross section and can detect clots. It is rarely used for DVT as it is more difficult to interpret and is time consuming. The CT scan is more useful for finding blood clots in the lung.
  • Magnetic Resonance Venography: Though very accurate, this test is usually reserved for patients in whom venography is needed but can’t be done for some reason like an allergy to the contrast dye.

Deep Vein Thrombosis Treatment

DVT is usually treated with anticoagulants, often called blood thinners. These are medications that prevent more clots and help prevent the clot from traveling to the lung and causing a pulmonary embolism:

  • Unfractionated heparin can be given as an injection or through an IV line.
  • Low-molecular weight heparins include dalteparin (Fragmin), enoxaparin (Lovenox), Tinzaparin (Innohep). These are drugs that are injected under the skin to stop new clots from forming.
  • Fondaparinux (Arixtra) is a different class of anticoagulants that is injected beneath the skin while waiting for warfarin (Coumadin) to take effect.
  • Warfarin is a pill that helps prevent the blood from clotting. It may take a few days to work. It is usually started along with heparin, low molecular weight heparin or fondaparinux to give it time to become effective. The other medicine is then stopped once the warfarin starts to work. The dose is different for each person, and a blood clotting test must be checked often since diet, activity, and other drugs can affect warfarin.
  • Apixaban (Eliquis), dabigatran (Pradaxa), edoxaban (Savaysa), and rivaroxaban (Xarelto) are newer pills that can be used instead of warfarin to treat DVT.


How long someone takes blood thinners depends on many factors including how the clot developed. If there were temporary risk factors, for example a long trip or recent immobility because of injury or illness, treatment may last 3-6 months. However, if the cause is unknown, you have a condition such as cancer that can cause blood clots, or there is a recurrent clot, medication may be required for more than 12 months.

Sometimes the doctor will inject clot-dissolving drugs called thombolytics. This has a higher chance of complications than using blood-thinning drugs and is usually reserved for life-threatening conditions.

Not all DVTs require blood thinners. Because small clots located in veins below the knee have a low risk of traveling to the lung, people with them may only be watched by the doctor. Using ultrasound tests of the veins, the clot can be monitored to see whether it is growing.

If the patient can’t use anticoagulants, or has recurrent blood clots even while on them, the doctor may place a filter in the blood vessel called the vena cava. The filter catches new clots before they can travel to the lungs but does not keep new clots from forming.

Compression stockings are useful in preventing a complication of a leg blood clot called postthrombotic syndrome or postphlebitis syndrome in which the leg swells and becomes painful. These stockings may be bought over-the-counter or can be custom fitted. Your doctor can tell you how long to wear them.

Next Steps

A person who has had a deep vein thrombosis may need follow-up Doppler ultrasounds or other tests if the leg swelling persists or if the symptoms come back. During anticoagulant treatment, it is often advised to take the following measures:

  • Take the prescribed amount of medication. Do not miss or add doses.
  • Follow the doctor's instructions closely about when to get lab tests for blood coagulation.
  • Ask the doctor before starting or stopping any medication, including over-the-counter medications. Many medicines increase or otherwise interfere with the effect of anticoagulants.
  • Ask what foods should be monitored because some foods may change the effectiveness of blood-thinning drugs.
  • Wear a Medic-alert bracelet with information about any anticoagulants that you are taking.
  • Inform any other medical professionals including dentists or podiatrists that you are taking an anticoagulant before undergoing any procedure.


Deep Vein Thrombosis Prevention

The key to prevention is to reverse any risk factors, for example:

  • If a person is obese, lose weight.
  • Avoid periods of prolonged immobility.
  • Keep the legs elevated while sitting down or in bed.
  • Avoid high-dose estrogen pills, unless they are deemed necessary by your doctor.

If you have had surgery recently, preventive treatment may be prescribed to avoid formation of a clot.

  • You may be instructed to get out of bed several times a day during the recovery period.
  • Sequential compression devices (SCDs) may be placed on the legs. Their squeezing action has been shown to reduce the probability of clot formation. You also may be given elastic stockings to wear.
  • Treatments such as low-molecular-weight heparin or low-dose warfarin may be prescribed to prevent clot formation.


Many DVTs will get better without further problems. Some people will develop a condition called post-phlebitic syndrome that involves continued swelling and pain.

If a person has had one deep vein thrombosis, they are more likely than the average person to have another deep vein thrombosis. One third of all people who have DVT will have another one within 10 years.

WebMD Medical Reference from eMedicineHealth Reviewed by Jennifer Robinson, MD on April 13, 2015



EMedicineHealth: "Deep Vein Thrombosis."

Family Practice Notebook: "Pulmonary Embolism." "Deep Vein Thrombosis (DVT)."

© 2015 WebMD, LLC. All rights reserved.