There are a number of factors that increase a person’s risk of developing a deep vein thrombosis.

If a person is found to have a DVT and there is no known medical condition or recent surgery that could have caused the DVT, it is possible that an inherited condition is the cause. This is especially true in people with a family member who has also experienced a DVT or pulmonary embolism. In these cases, testing for an inherited thrombophilia may be recommended. However, finding an inherited thrombophilia does not change the way that doctors treat the venous thromboembolism, and may not increase the chance of the blood clot coming back.

Medical conditions or medications — Some medical conditions and medications increase a person’s risk of developing a blood clot:




Heart failure

Previous DVT or pulmonary embolism (PE)

Increased age

Cancer – Some cancers increase substances in the blood that cause blood to clot.

Kidney problems, such as nephrotic syndrome

Certain medications (eg, some birth control pills, hormone replacement therapy, erythropoietin, tamoxifen, thalidomide). The risk of a blood clot is further increased in people who use one of these medications, and also have other risk factors.

Surgery and related conditions — Surgical procedures, especially those involving the hip, pelvis, knee, brain, or spine, as well as trauma (especially if blood vessels are injured) increase a person’s risk of developing a blood clot. During the recovery period, this risk often continues because the person is less active. Inactivity during long trips can also increase a person’s risk of developing a blood clot. Precautions to reduce the risk of blood clots are discussed below

Acquired thrombophilia — Some types of thrombophilia are not inherited, but can still increase a person’s risk of developing a blood clot.

Certain disorders of the blood, such as polycythemia vera or essential thrombocythemia

Antiphospholipid antibodies (antibodies in the blood that can affect the clotting process)

Inherited thrombophilia — Inherited thrombophilia refers to a genetic problem that causes the blood to clot more easily than normal. Various factors in the blood clotting process may be involved, depending on the type of genetic problem present.

An inherited thrombophilia is occasionally present in people with a venous blood clot (ie, thrombus). For example, deficiencies of antithrombin, protein C, or protein S can be found in less than 5 percent of patients who have had an unprovoked venous blood clot (a blood clot not caused by a medical or surgical condition). Other factors, such as factor V Leiden or the prothrombin gene mutation, can occur in approximately 20 to 25 percent of people with a venous blood clot. However, factor V Leiden or the prothrombin gene mutation is also found in up to 5 percent of otherwise healthy Caucasians. Venous thrombosis is infrequent before adolescence in people with inherited thrombophilia.