A Cohort Study to Test That There is a Low Risk of Recurrent VTE in Patients With a First Episode of Unprovoked VTE Who Stop Anticoagulant Therapy After 3 Months of Treatment in Response to Negative D-dimer Testing

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