The diagnosis and development of heparin-induced thrombocytopenia. Clinical and biological 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, oc cur early, mild and transitory. Type II HIT which is immunoallergic in natu re is the most important complication of this treatment. The thrombocytopen ia has a different presentation, acute with a fall in platelets over 30 per cent and is often associated with the occurence or worsening of a venous o r arterial thrombotic episode. The major problems of this secondary type ar e threefold. its recognition, its confirmation and its management should be as ear ly as possible to avoid the development of often dramatic complicat ions which compromise the prognosis. Laboratory investigations are required by highly reliable specialist laboratories following a careful clinical hi story. The natural history of the platelet count should enable rite difficu lt 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 w ith the benefit of large experience have just been obtained in France with marketing approval (AMM) for the management of HIT. danaparoid (Orgaran(R)) and recombinant hidurin, lepirudin (Refludan(R)). A declaration to the reg ional drugs monitoring center should not be omitted. In addition, each pati ent should be given a certificate confirming the immunallergy thus avoiding any further exposure with potentially dramatic consequences.