Deep venous thrombosis is a condition in which a blood clot forms in a vein that is deep inside the body.

Deep venous thrombosis (DVT) mainly affects the veins in the lower leg and thigh. A clot (thrombus) forms in the larger veins of the area. This clot can interfere with blood flow, and it may break off and travel through the bloodstream (embolize). The traveling blood clot (embolus) can lodge in the brain, lungs, heart, or other area, severely damaging that organ.

Risks for DVT include prolonged sitting (such as on long plane or car trips) or bedrest. It also may be caused by recent surgery (especially hip, knee, or female reproductive organ surgery), fractures, childbirth within the last 6 months, and the use of medications such as estrogen and birth control pills.

Risks also include overproduction of red blood cells in bone marrow (polycythemia vera), cancerous (malignant) tumor, and having a condition in which the blood is more likely to clot (hypercoagulability).

Deep venous thrombosis is most common in adults over age 60, but it can occur in any age group.

• Leg pain in one leg
• Leg tenderness in one leg
• Swelling (edema) of one leg
• Increased warmth in one leg
• Changes in skin color (redness) in one leg

An exam may show a red, swollen, or tender leg.

The presence of deep venous thrombosis may be seen on:

• X-rays to show veins (venography) in the legs
• Doppler ultrasound exam of a limb
• Plethysmography of the legs
• D-dimer blood test

• Antithrombin III, protein C, protein S
• Factor V Leiden
• Prothrombin 20210a mutation
• DIC screening
• Lupus anticoagulant and anticardiolipin antibodies

DVT treatment helps prevent a pulmonary embolus from forming and helps prevent another DVT.

For years, the standard treatment has been a medication called heparin to stop blood clots from forming (anticoagulant). Heparin is given through the vein. It results in quick anticoagulation and it treats the clot. A person with DVT also may get an oral medication called warfarin with the heparin.

Warfarin usually takes several days to fully work. Heparin is continued until the warfarin has been fully effective for at least 24 hours. People will take warfarin for about 6 months. Usually warfarin is started after heparin.

Because heparin is given continuously through a vein (IV), it requires a hospital stay. However, newer forms of heparin known as low molecular-weight heparin (usually a drug called enoxaparin) can sometimes be used. This heparin can be given by injection once or twice a day to shorten or avoid the need for a hospital stay.

Warfarin causes an increase in the time it takes blood to clot, known as prothrombin time (PT). A system called the International Normalized Ratio (INR) is used to report the ability of the blood to clot properly. Doctors will adjust warfarin to keep the INR between 2 and 3.

Most DVT's disappear without a problem, but they can recur. Some people may have chronic pain and swelling in the leg, known as post phlebitic syndrome. Pulmonary embolus is uncommon when DVT's are treated properly, but it can occur and can be life threatening.

• Pulmonary embolus
• Post-phlebitic syndrome

Call your health care provider if you have DVT-like symptoms.

Go to the emergency room or call the local emergency number (such as 911) if you have DVT and you develop chest pain, difficulty breathing, fainting, loss of consciousness, or other severe symptoms.

Doctors may prescribe anticoagulants to help prevent DVT in high-risk people or those who are undergoing high-risk surgery. To help prevent DVT, move your legs often during long plane trips, car trips, and other situations in which you are sitting or lying down for long periods of time.