[Role of the hemostasis laboratory in the etiologic approach to deep vein thrombosis]. / Place du laboratoire d'hémostase dans la démarche étiologique des thromboses veineuses profondes.

Thrombophilia is characterized by an inherited or acquired defect in the blood coagulation pathway leading to an increased risk for thrombosis. The etiological approach following confirmed venous thrombotic events should rule out medical or chirurgical risk factors. Thrombophilia should be sought by laboratory tests. The recent discovery of a blood coagulation defect: inherited resistance to activated protein C which is found to 20% of patients with former thrombotic events has changed current laboratory approach. Deficiencies of one of the anticoagulant proteins (antithrombin III, protein C, protein S) are found in 10% of the patients, similar to the frequency of antiphospholipid antibodies. These tests may be difficult to interpret immediately after the thrombotic event because of various factors such as inflammatory states or anticoagulant treatments. Therefore this abnormal tests should be confirmed on a later sample analysis far from the event. The discovery of an inherited blood coagulation pathway defect may affect the duration of treatment, prophylaxis in situations with circumstantial risk factors and requires familial analysis. Inherited resistance to activated protein C may be associated with another inherited defect leading to an increased risk for thrombosis.