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.