Epidemiology of venous thromboembolism.

The annual incidence of diagnosed venous thromboembolism (VTE) is 1 to 2 events per 1000 of the general population. VTE is very uncommon before age 20 years and, after 40 years of age, the incidence about doubles with each decade. Over half of episodes of VTE are deep vein thrombosis (DVT), and three quarters are first episodes. The incidence of VTE is similar in men and women and lower in Asians than it is in Caucasians or Africans. Hereditary risk factors include the factor V Leiden mutation; the G20210A prothrombin gene mutation; and deficiencies of protein C, protein S, and antithrombin. Hyperhomocysteinemia and elevated levels of factors I, VIII and XI, which may be hereditary and/or acquired, are also risk factors. Acquired risk factors include malignancy, hospitalization, surgery, venous trauma, immobilization, estrogen therapy, pregnancy, and the antiphospholipid antibodies. Risk factors for a first episode of VTE are generally also risk factors for recurrence, although the associated relative risk for thrombosis may differ for a first and subsequent event.