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Identifying unprovoked thromboembolism patients at low risk for recurrence who can discontinue anticoagulant therapy

From the Thrombosis Program, Division of Hematology, Department of Medicine (Rodger, Wells, Ramsay, Betancourt), University of Ottawa; Clinical Epidemiology Unit, Ottawa Health Research Institute (Rodger, Wells, Ramsay, Betancourt), The Ottawa Hospital, Ottawa, Ont.; Department of Medicine (Kahn, Solymoss), McGill University, Montréal, Que.; Centre for Clinical Epidemiology and Community Studies (Kahn), Jewish General Hospital, Montréal, Que.; Department of Medicine (Anderson), Dalhousie University, Halifax, NS; Department of Medicine, Hôpital du Sacré-Coeur de Montréal (Chagnon), University of Montreal, Montréal, Que.; University Hospital and the Department of Internal Medicine and Chest Diseases (Le Gal), Brest, France; Department of Medicine, Michael G. DeGroote School of Medicine (Crowther), McMaster University, Hamilton, Ont.; Department of Internal Medicine, Geneva University Hospital, and the Faculty of Medicine (Perrier), Geneva, Switzerland; Department of Medicine, UC Davis School of Medicine (White), Sacramento, Calif.; Department of Medicine, St. Paul's Hospital (Vickars), University of British Columbia, Vancouver, BC; Division of Hematology, Department of Medicine (Kovacs), University of Western Ontario, London, Ont.

Correspondence to: Dr. Marc Rodger, Division of Hematology, The Ottawa Hospital, General Campus, 501 Smyth Rd., Ottawa ON K1H 8L6; fax 613 739-6102; mrodger{at}ohri.ca

Background: Whether to continue oral anticoagulant therapy beyond 6 months after an "unprovoked" venous thromboembolism is controversial. We sought to determine clinical predictors to identify patients who are at low risk of recurrent venous thromboembolism who could safely discontinue oral anticoagulants.

Methods: In a multicentre prospective cohort study, 646 participants with a first, unprovoked major venous thromboembolism were enrolled over a 4-year period. Of these, 600 participants completed a mean 18-month follow-up in September 2006. We collected data for 69 potential predictors of recurrent venous thromboembolism while patients were taking oral anticoagulation therapy (5–7 months after initiation). During follow-up after discontinuing oral anticoagulation therapy, all episodes of suspected recurrent venous thromboembolism were independently adjudicated. We performed a multivariable analysis of predictor variables (p < 0.10) with high interobserver reliability to derive a clinical decision rule.

Results: We identified 91 confirmed episodes of recurrent venous thromboembolism during follow-up after discontinuing oral anticoagulation therapy (annual risk 9.3%, 95% CI 7.7%–11.3%). Men had a 13.7% (95% CI 10.8%–17.0%) annual risk. There was no combination of clinical predictors that satisfied our criteria for identifying a low-risk subgroup of men. Fifty-two percent of women had 0 or 1 of the following characteristics: hyperpigmentation, edema or redness of either leg; D-dimer 250 µg/L while taking warfarin; body mass index 30 kg/m²; or age 65 years. These women had an annual risk of 1.6% (95% CI 0.3%–4.6%). Women who had 2 or more of these findings had an annual risk of 14.1% (95% CI 10.9%–17.3%).

Interpretation: Women with 0 or 1 risk factor may safely discontinue oral anticoagulant therapy after 6 months of therapy following a first unprovoked venous thromboembolism. This criterion does not apply to men. (http://Clinicaltrials.gov trial register number NCT00261014)

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