The risk of recurrent venous thromboembolism among patients with high factor IX levels.

High factor IX (FIX) is a risk factor of deep vein thrombosis. The impact of high FIX on the risk of recurrent venous thrombosis is unknown. We prospectively followed 546 patients after anticoagulation for a first spontaneous venous thromboembolism. Patients with a natural coagulation inhibitor deficiency, lupus anticoagulant or cancer were excluded. At 3 years, the likelihood of recurrence was 23% among patients with high FIX (exceeding the 75th percentile) compared with 11% among patients with lower levels. Among patients with high FIX, the relative risk of recurrence was 2.2 (95% CI: 1.3-3.6) before and was 1.6 (95% CI: 1.0-2.8) after adjustment for age, gender, duration of anticoagulation, FV Leiden, FII G20210A, high FVIII and hyperhomocysteinemia. Compared with patients with low factor IX (< 138 IU dL(-1)) and low FVIII (