Purpose: To determine the cost-effectiveness, in the UK, of thrombophilia testing in patients following idiopathic venous thromboembolism (VTE) with reference to extending the duration of warfarin treatment.

Methodology: Literature reviews were undertaken to estimate the following parameters: the average risk of recurrent VTE (either pulmonary embolism (PE) or deep vein thrombosis (DVT)), by sex, following initial VTE; the increased risk associated with each type of thrombophilia; and the risks of haemorrhage, by age group, associated with warfarin treatment. A systematic review of economic evaluations of thrombophilia testing was undertaken alongside reviews of the costs, utilities and mortality associated with PE, DVT and haemorrhage events. A discrete event simulation model was constructed to estimate the timing of the next event, defined as VTE, haemorrhage or death through other causes. Patients with recurrent VTE were assumed to receive lifelong warfarin. Patients who haemorrhaged whilst on warfarin had treatment discontinued; were these patients to have a subsequent VTE, warfarin treatment would be re-initiated providing that the previous haemorrhage was not intracranial.

Four durations of warfarin treatment were simulated: 3 months (base case), 10 years, 20 years and lifelong. The net benefit of each strategy compared with 3 months treatment was calculated for each thrombophilia type assuming a MAICER of £20,000 per QALY. Thrombophilia testing was deemed cost-effective in age and sex sub-groups,where the summated net benefit, weighted by thrombophilia type, was greater than the costs of the tests.

Results: Due to the higher risk of recurrence in males, the greater risk of a subsequent VTE being fatal following PE rather than DVT, and the increased risk of haemorrhage in elderly patients, the cost-effectiveness of thrombophilia testing varied substantially amongst population sub-groups. It was cost-effective to undertake thrombophilia testing in all patients with a previous PE. In patients with a previous DVT it was cost-effective to test males aged below 70 and females aged below 50 years. The matrix of 'optimal' warfarin duration by patient sub-group and thrombophilia type will be presented.

Conclusions: Thrombophilia testing following an idiopathic VTE is cost-effective, except in women aged 50 years or older and men aged 70 years or older, who present with a DVT.