Prediction of recurrent venous thromboembolism by the activated partial thromboplastin time

BACKGROUND: Venous thromboembolism (VTE) is a multi-factorial disease. Extensive thrombophilia screening is costly and often inconclusive. Simple laboratory methods are required to predict the risk of recurrence. OBJECTIVE: To assess if measurement of activated partial thromboplastin time (APTT) allows stratification of patients with VTE into high- and low-risk categories with regard to recurrence. PATIENTS AND METHODS: We prospectively followed 918 patients with a first unprovoked VTE and studied the relationship between recurrence and an APTT after discontinuation of anticoagulation. APTT was expressed as a ratio of test to reference coagulation times. Study endpoint was symptomatic recurrent VTE. RESULTS: Venous thromboembolism recurred in 101 (11%) patients. Patients without recurrence had a greater APTT ratio than those with recurrence (0.97 +/- 0.09 vs. 0.93 +/- 0.09, P = 0.001). After 4 years, probability of recurrent VTE was 8.5% (95% CI: 5.5-11.5%) among patients with a ratio equal to or > 0.95 and 15.6% (95% CI: 11.4-19.9%) among patients with a lower ratio (P = 0.005). Compared with patients with an APTT ratio < 0.95, the relative risk (RR) of recurrence among patients with a ratio equal to or > 0.95 was 0.56 (95% CI: 0.38-0.84, P = 0.005) before and 0.58 (95% CI: 0.39-0.87, P = 0.009) after adjustment for sex, age, factor V Leiden, and factor II G20210A. CONCLUSIONS: Measurement of APTT allows stratification of patients with VTE into high- and low-risk categories with regard to recurrence.