[Heparin-associated thrombocytopenia: successful therapy of patients after prospective selection of a compatible heparinoid with the heparin-induced platelet activation test].

Diagnosis of HAT type II and treatment of thromboembolic complications in these patients are difficult. Recently we have developed the heparin-induced platelet activation (HIPA) assay which allows a rapid confirmation of the tentative diagnosis of HAT type II. In vitro studies with sera of 25 patients revealed cross-reactivity to the LMW heparins Fragmin, Fraxiparin and Clexane whereas a LMW heparinoid, Org 10172 (Orgaran), did not. In a prospective study this heparinoid was selected for 10 HAT patients, for whom further parenteral anticoagulation was required. In 7 of these patients who received LMW heparins prior to laboratory investigations low platelet counts persisted under treatment with LMW heparins and 2 patients developed additional thromboembolic complications. Upon treatment with Org 10172 platelet counts normalized in 9 patients, in 1 patient thrombocytopenia was unrelated to parenteral anticoagulation, in 1 patient platelet count normalized after discontinuation of Org 10172. We conclude that the HIPA assay allows the laboratory diagnosis of HAT type II and the selection of a compatible heparin or heparinoid for further parenteral anticoagulation.