In patients aged less than 45 with a true idiopathic lower limb deep vein thrombosis (DVT), the chance of finding an inherited thrombophilia is less than 50%, but for pulmonary embolism this falls to less than 10%. The chances of finding a prothrombotic state are much lower if the patient is older or the DVT provoked. As detecting a prothrombotic state should not alter treatment decisions, some investigators have cautioned against undertaking these studies in patients with venous thromboembolism.¹ Most UK haematologists agree that prothrombotic tests should be targeted at patients aged less than 50 with unexpected or recurrent venous thrombosis; and these tests are undertaken by most district haematology departments. However, the tests are expensive, with a thrombophilia screen …