What causes deep vein thrombosis?
Deep vein thrombosis is caused by blood clots in blood vessels which form in veins where blood flow is sluggish or has been disturbed, in pockets in the calf's deep veins, or in veins that have been traumatized. Symptoms include swelling and tenderness of the calf or thigh, and possibly warmth. Only 23–50% of patients experience symptoms, so it's often "silent."
Some individuals and families have underlying clotting tendencies that can be tested for.
Three main factors (known as Virchow's triad) can contribute to deep vein thrombosis: injury to the vein's lining, an increased tendency for blood to clot, and slowing of blood flow.
Veins may be injured during surgery, by injection of irritating substances, or by certain disorders, such as Buerger's disease. They may also be injured by a clot, making formation of a second clot more likely.
Some disorders, such as disseminated intravascular coagulation, cause blood to clot when it should not. Some cancers and, rarely, use of oral contraceptives can cause blood to clot more readily. Sometimes blood clots more readily after childbirth or surgery. Among older people, dehydration and smoking are common causes of this tendency and can therefore contribute to deep vein thrombosis.
During prolonged bed rest, blood flow slows, because the calf muscles are not contracting and squeezing the blood toward the heart. For example, deep vein thrombosis may develop in people who have had a heart attack and lie in hospital beds for several days without sufficiently moving their legs or in people whose legs and lower body are paralyzed (paraplegics). Deep vein thrombosis can develop after hip repair or replacement. Thrombosis can even occur in healthy people who sit for long periods, for example, during long drives or airplane flights. |
