D-Dimer Guided Oral Anticoagulant Treatment (OAT)

Inclusion Criteria: To be enrolled in this study, patients must: * have an objectively confirmed first episode of unprovoked VTE or of VTE during a minor transient risk factor. Minor transient risk factors include 6 weeks of estrogen therapy, prolonged air travel (i.e., \> 6 hours), pregnancy, less marked leg injuries or immobilization without injury or surgical intervention * be scheduled to receive oral anticoagulant treatment for at least 3 months * be willing to be randomized * be willing to participate for the full duration of the study Exclusion Criteria: * pregnancy or breast feeding * contraindications against OAT (i.e., intracranial hemorrhage, subarachnoid hemorrhage, hemorrhagic stroke) * age \< 18 years * presence of antiphospholipid antibodies or any other thrombophilic risk factor requiring long-term OAT (i.e., antithrombin deficiency, hereditary PC deficiency) * poor patient compliance