What Is Deep Vein Thrombosis?

Deep vein thrombosis (throm-BO-sis) is a blood clot that forms in a vein deep in the body. Most deep vein clots occur in the lower leg or thigh. They also can occur in other parts of the body.

If a clot in a vein breaks off and travels through your bloodstream, it can lodge in your lung. This is called pulmonary embolism (PUL-mo-ner-e EM-bo-lizm), which is a very serious condition that can cause death. Blood clots in the thigh are usually more likely to break off and cause pulmonary embolism than clots in the lower leg or other parts of the body.

A blood clot also can occur in veins that are close to the surface of the skin. This type of blood clot is called superficial venous thrombosis or phlebitis (fle-BI-tis). Blood clots in superficial veins are not dangerous because they can’t travel to the lungs.