Risk of recurrent venous thromboembolism related to prior risk situations: re-evaluation of a cohort study with a longer follow-up

Venous thromboembolism (VTE) is a chronic disease. Strategies to assess groups at a high risk of recurrence are needed. We reported that patients without prior risk situation for VTE had an incidence rate ratio (IRR) three times higher when compared with those with this history. The aim of this study was to re-evaluate the cohort, with a longer follow-up and evaluated the association between the absence of a prior risk situation for VTE with an increased risk for recurrence. A total of 289 patients with a previous VTE were followed for 116 months. Patients were advised to attend the outpatients’ clinic in case of suspected VTE recurrence. Incidence rates of recurrent thrombotic events were calculated as the number of events over the accumulated observation time. Recurrent VTE occurred in 52 (18%) patients. Patients with a provoked first event and positive prior risk situations for VTE had an incidence rate for recurrence of 1.2 [95% confidence interval (95% CI), 0.7–1.9] per 100 patient-years. The IRR of this subgroup compared with patients with a provoked event without prior risk situations for VTE was 0.9 (95% CI 0.4–2.4). IRR was 2.5 (95% CI, 1.3–4.9) in patients with an unprovoked event and positive prior risk situations and 5.9 (95% CI, 32.8–12.5) in patients with an unprovoked event and no prior risk situations compared with patients with a provoked event without other prior risk situations for VTE. Exposure to prior risk situations for VTE was a protective factor among those patients whose first VTE event was unprovoked.