Incident thrombus location and predicting risk of recurrent venous thromboembolism.

Background: Understanding venous thromboembolism (VTE) recurrence risk is central to determining the appropriate treatment course. Whether this risk varies after discontinuing anticoagulation or overall by type of incident event (pulmonary embolism [PE] vs deep vein thrombosis [DVT]) and by the detailed location of the DVT needs further clarification. Methods: In this population-based inception cohort of incident VTE cases with follow-up by electronic health record review, incident DVT was categorized as distal, popliteal, or iliofemoral. We used the Fine-Gray regression model to describe the predictive association of the thrombus location with the risk of recurrence before death. Results: Among 2766 participants with an incident event from 2002 to 2010, 1713 (62%) ceased anticoagulation and were followed for recurrent events; 301 events were observed during the 4.5 years of follow-up. Relative to participants with an incident thrombus in an iliofemoral location and no PE, those with a thrombus in a popliteal location and no PE had a similar risk of recurrence (adjusted subdistribution hazard ratio [aSHR], 0.82 [95% confidence interval (CI), 0.57-1.19]), while those with a thrombus in a distal location and no PE and those with a thrombus that included a PE had lower risk of recurrence: aSHR, 0.34 (95% CI, 0.20-0.57); and aSHR, 0.58 (95% CI 0.45-0.76), respectively. Conclusions: The findings of this population-based inception cohort confirm that the risk of recurrent VTE after discontinuing anticoagulants is similar after iliofemoral and popliteal DVT but is lower after distal DVT. Recurrence may be lower after PE than proximal DVT.