Which patients should be investigated for thrombophilia?

Testing for heritable thrombophilia is not indicted in unselected patients presenting with venous thrombosis. Table 39.1 summarises factors which should prompt consideration of thrombophilia. Accurate history taking is essential; particular attention should be given to the nature of the recent thrombotic event, the presence of known risk factors (Table 39.2), a previous history of thrombosis and the family history. Definition of a ‘positive’ family history of thrombosis is problematic. If we use the simple definition of a history of deep vein thrombosis (DVT) or pulmonary embolus (PE) in a first or second degree relative, then approximately 25% of all patients will have a positive family history. Even among those with a strong family history only a small minority will have a cause of inherited thrombophilia identified.

Basic investigations of thrombophilia should include a blood count (to exclude polycythaemia and other myeloproliferative disorders) and a coagulation screen. Further laboratory testing is dictated by the possible causes of familial and acquired thrombophilia detailed below. Testing for thrombophilia should not be undertaken during an acute episode of venous thromboembolism when low levels of coagulation inhibitors are routinely found. Systemic disorders such as liver disease or disseminated intravascular coagulation (DIC) can depress the levels of coagulation inhibitors and thus simulate the laboratory abnormalities found in familial thrombophilia.

Familial thrombophilia