Past provoking venous thrombosis risk situations on the risk of a recurrent thrombotic event: a cohort study.

OBJECTIVE: Strategies that can classify the risk for recurrent venous thrombosis are needed. Some patients may have experienced many risk situations during their life time without developing venous thrombosis (VT), while others may have experienced few of such risk factors and then develop VT idiopathically or after a single provoked risk factor. We hypothesized that those who had 'survived' many risk situations without developing VT would, after a first VT, have a low recurrence risk. METHODS: Brazilian tertiary hospital cohort was followed for an average of 30 months after anticoagulation withdrawal for a first VT. Patients with indication for indefinite anticoagulation were not included. The primary end point was objective recurrent VT. RESULTS: Recurrent VT was recorded in 7% of 378 eligible patients. Patients with a provoked first event and positive past risk situations for VT had an incidence rate of recurrence of 1.16 (95% confidence interval [CI], 0.47-2.39) per 100 patient-years. The incidence rate ratio (IRR) of this subgroup compared to patients with a provoked event without other past risk situations for VT was 1.1 (95% CI, 0.3-4.4). This IRR was 3.3 (95% CI, 1.3-8.7) in patients with an unprovoked event and positive past risk situations and 5.1 (95% CI, 1.6-16.1) in patients with an unprovoked event and no past risk situations. CONCLUSIONS: Asking a patient about past exposure of venous thrombosis risk factors long before the occurrence of a first venous thrombosis occurred, does not provide information to classify patients at lower risk for recurrence of venous thrombosis.