Deep vein thrombosis is the formation of a blood clot (thrombus) in a deep, interior vein (as opposed to varicose veins). When a vein is inflamed (phlebitis) it often forms a thrombus, which restricts blood flow through the vein. A portion of the clot can break away and travel through the veins to the lungs. Blockage of a large vessel in the lungs, called a pulmonary embolism, may cause serious complications and possibly death. Click here to see how clots form.


Blood clots most commonly occur when there is trauma to the vessel, hypercoagulability and stasis (Virchow’s Triad). This damage is often a result of infection, surgery, or a previous thrombosis. When damage occurs, blood clots can develop, usually starting in the veins of the calf progressing upward.
If the blockage is not treated, it can jeopardize an affected limb by obstructing blood flow. This causes leg swelling and can lead to chronic venous insufficiency (CVI), when the same clotting factors that stop external bleeding begin to function inappropriately in deep veins. The clot may grow large enough to block the vein, or become dislodged and travel to the lungs.
Less common causes of thrombosis are:

  • Lengthy periods of immobility (such as sitting on an airplane or confinement to bed or wheelchair). These can disrupt the balance of blood pressure in the veins, slow circulation and impair blood flow.
  • Clotting abnormalities associated with cancer, sickle-cell anemia, estrogen or progestin replacement therapy, dehydration and thickening of the blood.
Warning Signs

Approximately half of those with deep vein thrombosis never have recognized symptoms. The symptoms are:

  • Sudden, continuous deep pain in the calf or thigh
  • Deep pain in a leg which increases, either when exercising or from standing for long periods
  • Redness of the skin
  • Swelling
  • Warm skin
  • Leg fatigue
  • Surface veins become more visible

DVT is the most common cause of cardiovascular death, after strokes and myocardial infarctions (heart attacks).
deep vein thrombosis or blood clot

Treatment & Prevention

Thrombosis in varicose or superficial veins is normally treated with anti-inflammatory drugs, together with elevating the legs to reduce pressure. Deep vein thrombosis is immediately treated with anticoagulants (blood thinners), together with bed rest and elevation of the legs above heart level to reduce pressure and promote the flow of blood back to the heart. If blood thinners are used for long-term treatment, patients are cautioned not to take certain other medications, especially aspirin, which may interact with them. When a patient resumes walking, elastic compression of the lower leg controls swelling, collapses the superficial veins and increases blood flow in the deep veins to promote healing. If there is an associated venous ulcer of the ankle, this same treatment promotes healing. People who are vulnerable to blood clots should not smoke, because tobacco promotes clot formation.