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