Deep vein thrombosis (DVT) is a blood clot (thrombus) in a deep vein, usually in the legs.
Clots can form in superficial veins and in deep veins. Blood clots with inflammation in superficial veins (called superficial thrombophlebitis or phlebitis) rarely cause serious problems. But clots in deep veins (deep vein thrombosis) require immediate medical care.
These clots are dangerous because they can break loose, travel through the bloodstream to the lungs, and block blood flow in the lungs (pulmonary embolism). Pulmonary embolism is often life-threatening. DVT can also lead to long-lasting problems. DVT may damage the vein and cause the leg to ache, swell, and change color.
Blood clots most often form in the calf and thigh veins, and less often in the arm veins or pelvic veins. This topic focuses on blood clots in the deep veins of the legs, but diagnosis and treatment of DVT in other parts of the body are similar.
Each year in the United States, between 350,000 and 600,000 people get a blood clot in the legs or in the lungs.