D-dimer to Select Patients With First Unprovoked Venous Thromboembolism Who Can Have Anticoagulants Stopped at 3 Months

Inclusion Criteria: 1. Be \>= 18 years of age 2. Have had ONE episode of unprovoked proximal DVT and/or PE 3. Have completed 3 uninterrupted months of warfarin therapy (target INR of 2.0-3.0) Exclusion Criteria: 1. Another indication for long-term anticoagulation (e.g., atrial fibrillation) 2. A high risk of bleeding as evidenced by any of the following: * Age greater than 75 years * Previous episode of major bleeding where the cause was not effectively treated * Known chronic thrombocytopenia with a platelet count of less than 120,000 x 10\^9 /L * Known chronic renal impairment with a creatinine of more than 150 mumols /litre (1.7 mg/dl) * Known chronic liver disease with a total bilirubin of more than 25 mumols /litre (1.5 mg/dl) * Active peptic ulcer disease * Poor compliance with, or control of, anticoagulant therapy during initial treatment * Requires dual antiplatelet therapy (e.g. aspirin and clopidogrel) 3. A vena caval filter 4. Has had D-dimer testing performed within 2 months of potential enrollment other than for evaluation of suspected recurrent VTE that was not confirmed 5. Has a life expectancy less than 5 years 6. Is unable to attend follow-up visits because of geographic inaccessibility 7. Is participating in a competing clinical investigation