Table 1 Study inclusion and exclusion criteria

Inclusion criteria

People aged 18 years or over with a diagnosis of first unprovoked^* proximal^** DVT or PE on treatment with anticoagulants

Have completed 3 – 6 months of anticoagulant therapy (target 2–3)

^*The episode will be defined as unprovoked as long as there is no history within the previous 3 months of:

major surgery; lower limb trauma e.g. fracture, cast, limping for 3 days; use of the combined oral contraceptive pill or hormone replacement therapy ; pregnancy; significant immobility e.g. confined to bed for 3 days; active cancer.

^**Proximal refers to a DVT alone in the trifurcation area, popliteal, superficial femoral, deep femoral, common femoral and iliac veins.

Exclusion criteria

Patients under the age of 18 years

Patients with another indication for long term warfarin therapy e.g. Atrial Fibrillation

Patients with a diagnosis of first unprovoked proximal DVT or PE who are no longer on anticoagulation therapy

Patients with a high risk of bleeding as evidenced by any of the following:

• Patients with a previous episode of major bleeding where the cause was not effectively treated

• Known thrombocytopaenia with a platelet count of less than 120 ×10⁹ /L

• Known chronic renal failure with a creatinine of more than 150 μmols/L (1.7 mg/dl) or eGFR less than 30

• Known chronic liver disease with a total bilirubin of more than 25μmols/L (1.5 mg/dl)

• Active peptic ulcer

• Patients requiring antiplatelet therapy (eg Aspirin and/or Clopidogrel)

Patients with a vena cava filter in place

Patients who have had a D–dimer test performed within 2 months of potential enrolment other than for evaluation for suspected recurrent VTE that was not confirmed

Patients whose GP expects their life expectancy to be less than 5 years

Patients unable to attend follow up visits due to geographic inaccessibility

Patients participating in a competing investigation

Patients with known antiphospholipid syndrome

If patients are subsequently found to have antiphospholipid syndrome then they will have to be excluded.

Patients with known inherited protein C and/or protein S or antithrombin deficiency

If patients are subsequently found to have protein C and/or protein S or anithrombin deficiency then they will have to be excluded.

Patients with a diagnosis of active cancer

Patients unwilling to give consent