Venous thrombosis is an obstruction of a venous blood vessel by a clot (thrombus). The migration of all or part of the clot from the vein to a pulmonary artery causes pulmonary embolism. The incidence of these thromboembolic events is around 3 per 10 000 per year in people aged between 25 and 35 and increases with age. The causes are multiple and the triggers numerous. There are different types of thrombophilia – clotting abnormalities –, some inherited and others related to the presence of autoantibodies.

Venous thromboses occur as a result of a triggering event and in the presence of risk factors. When a patient suffers a venous thromboembolic event, testing for thrombophilia has no foreseeable impact on the nature or dosage of anticoagulant therapy. It is of no benefit when a transient triggering factor has been identified, since the low risk of recurrence does not justify prolonged anticoagulant therapy even in cases of detected thrombophilia.

When there is a high risk of recurrence which warrants prolonged anticoagulation treatment, the absence of detection of thrombophilia does not justify reducing the duration of the treatment. In this case, the limiting factor is the haemorrhagic risk.

In the event of thrombosis, in the absence of any other identified risk of recurrence, investigating whether there is hereditary thrombophilia when a family risk is likely or testing for antiphospholipid antibodies sometimes help decide whether or not to prolong anticoagulant therapy, although many uncertainties remain.

©Prescrire 1 May 2017

"Thrombophilia. Testing rarely useful after a venous thromboembolic event" Prescrire Int 2017; 26 (182): 129. (Pdf, subscribers only).