D-dimer Test to Establish Duration of Anticoagulation After a First Idiopathic Episode of Venous Thromboembolism; the Prospective Randomized "Prolong" Study

This is a multicenter prospective follow-up study in patients with a first episode of symptomatic idiopathic venous thromboembolism (proximal deep vein thrombosis and/or pulmonary embolism) who are treated with vitamin K antagonists (either warfarin or acenocoumarol) for a minimum of 3 months. Eligible patients who give informed consent are instructed to immediately stop oral anticoagulation and refrain from taking any other antithrombotic drugs until the next visit, scheduled after 30 days. At that visit, venous blood is sampled to perform D-dimer assay and thrombophilia tests. D-dimers are assessed using the Clearview Simplify D-dimer assay (Agen Biomedical Limited, Brisbane, Australia). Patients with normal D-dimer results do not continue anticoagulation, whereas those with elevated D-dimer results are randomized using a computer program to either stop or resume anticoagulation with vitamin K antagonists (INR 2.0-3.0). All patients are followed-up for 18 months. The study outcome are the composite of confirmed recurrent venous thromboembolism and major bleeding events. All suspected outcome events and all deaths are evaluated by a central adjudication committee whose members are unaware of the D-dimer and thrombophilia results and of the group assignments.