[Diagnosis and development of heparin-induced thrombocytopenia. Biological and clinical aspects].

Two types of thrombocytopenia occur during treatment with heparin: type I and type II heparin-induced thrombocytopenia (HIT). Type I HIT is due to a direct interaction between heparin and platelets. They are asymptomatic, occur early, mild and transitory. Type II HIT which is immunoallergic in nature is the most important complication of this treatment. The thrombocytopenia has a different presentation, acute with a fall in platelets over 30 per cent and is often associated with the occurrence or worsening of a venous or arterial thrombotic episode. The major problems of this secondary type are threefold: its recognition, its confirmation and its management should be as early as possible to avoid the development of often dramatic complications which compromise the prognosis. Laboratory investigations are required by highly reliable specialist laboratories following a careful clinical history. The natural history of the platelet count should enable the difficult diagnosis of HIT to be made more accurately. The treatment of confirmed HIT and/or symptomatic HIT often requires a multidisciplinary approach from a specialized team involving clinicians and hematologists. Two therapies with the benefit of large experience have just been obtained in France with marketing approval (AMM) for the management of HIT: danaparoid (Orgaran) and recombinant hidurin, lepirudin (Refludan). A declaration to the regional drugs monitoring center should not be omitted. In addition, each patient should be given a certificate confirming the immunallergy thus avoiding any further exposure with potentially dramatic consequences.