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Learn About Deep Vein Thrombosis/Blood Clots

Blood clotting is a normal process that prevents bleeding when a blood vessel is injured. When a blood clot forms in veins deep in the body it is called deep vein thrombosis (DVT). Most deep vein blood clots occur in the lower leg or thigh.

Key Facts

  • Blood clotting is normal but can be dangerous when inside a vein. Clots in veins deep in the body can break free, travel through the bloodstream and get stuck in the lungs, causing a pulmonary embolism.
  • Although most patients survive, these conditions can be serious and even deadly.
  • Treatment with blood thinners is usually effective.

What Is DVT and How Does It Affects Your Body?

When a blood clot forms in a vein deep in the body, it is called deep vein thrombosis or DVT. These deep vein blood clots can form anywhere in the body but are most common in the calf or thigh of the leg.

There are many different reasons why DVT can develop. Bone fractures, major surgery, and cardiac catheterization increase the chance of deep vein blood clot formation. Use of birth control pills, pregnancy, obesity, cigarette smoking, cancer, and chemotherapy can also increase a person’s risk of DVT.

Other common risks include:

  • Immobility resulting from hospitalization or prolonged sitting in one position (such as during air travel).
  • Injury to the blood vessel as a result of accident or trauma.
  • Hypercoagulation — an increased rate of clotting that can be an inherited defect or acquired condition.

A serious and potentially life-threatening complication of these blood clots. DVT is when a deep vein clot breaks loose and travels through the blood stream, lodging in the arteries in the lungs and blocking blood flow from the heart to the lungs. This is called a pulmonary embolism.

DVT can be life-threatening, but patients almost always survive. Prompt recognition and diagnosis can be lifesaving, as is prevention of other complications associated with this potentially fatal condition.

    This content was developed in partnership with the CHEST Foundation, the philanthropic arm of the American College of Chest Physicians.


    Reviewed and approved by the American Lung Association Scientific and Medical Editorial Review Panel. Last reviewed December 13, 2016.

    Page Last Updated: July 29, 2019

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