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Venous Thrombosis

Thrombosis (throm-BO-sis) refers to the formation of a blood clot in a blood vessel. While clots can form in an artery or a vein, this article focuses only on clots that occur in veins, called venous thrombosis.

The clot, or "thrombus," blocks or impairs blood flow in the vein, leading to symptoms and secondary complications.

Thrombosis can happen for no apparent reason, but it is often associated with an inherited predisposition to blood clots, surgical procedures, immobility, oral contraceptive use or underlying medical conditions. Medical conditions such as pregnancy, cancer, inflammatory bowel disease, certain rheumatologic disorders and obesity are known to increase your risk for thrombosis.

Thrombosis often occurs in the legs. When it affects the deep veins — rather than the superficial veins you can see under your skin — it is called a deep vein thrombosis (also called deep venous thrombosis), or DVT.

Embolism (EM-bo-lizm) refers to the sudden blockage of a blood vessel from a clot or other material. Unlike a thrombus that develops at the site of blockage, an embolism originates in one location in the body and travels to a second site where it causes the blockage. One of the more common types of embolism occurs in the lung, called a pulmonary embolism (PE). Pulmonary embolisms usually come from a deep vein thrombosis that formed in the leg or pelvic region, and they can be life threatening.

Our Approach to Venous Thrombosis

The main treatment for deep venous thrombosis, or blood clots that form in the deep veins, is anticoagulation therapy. Anticoagulant medications can prevent clots from forming and stop an existing clot from getting bigger, as the body works to clear the clot on its own. A small percentage of patients also need a filter inserted into the large vein that leads from the legs to the heart, to block any future clots from reaching the lungs. UCSF's world-class hematologists and interventional radiologists work together to provide expert insertion and removal of these filters.

For mothers-to-be who are at particular risk for blood clots, our hematology team works closely with UCSF obstetricians who specialize in high-risk pregnancy. This partnership provides the best possible treatment before, during and after pregnancy.

UCSF Health medical specialists have reviewed this information. It is for educational purposes only and is not intended to replace the advice of your doctor or other health care provider. We encourage you to discuss any questions or concerns you may have with your provider.