Pergamon Thrombosis Research, Vol. 81, No. 5, pp. 525-532, 1996 Copyright Q 1996 Elsevier Science Ltd Printed in the USA. All rights reserved 0049-3848/96 $12.00 + .X3 PI1 SOO49-3848(96)00027-S CROSS-REACTIVITY STUDY OF LOW MOLECULAR WEIGHT HEPARINS AND HEPARINOID IN HEPARIN-INDUCED THROMBOCYTOPENIA Chee M Vun, Sue Evans, Beng H Chong Department of Haematology, Prince of Wales Hospital, Sydney, New South Wales, Australia. (Received 3 October 1995 by Editor P.N. Badenhorst, revised/accepted 15 January 1996) Abstract Previous studies suggested that the cross-reactivity rates of low molecular weight (LMW) heparins with the antibody in heparin-induced thrombocytopenia (HIT) are more than 80%, whilst that of the LMW heparinoid (Orgaran) is relatively low at about 10%. These earlier studies were limited either in the number of patients studied, or in investigating only a single drug. They were also inadequate due to non-standardisation of testing conditions. This study compares three LMW heparins (Fragmin, Clexane, Fraxiparin) and a heparinoid (Orgaran) in their cross-reactivity rates with the HIT antibody. The sera of 45 HIT patients were tested using platelet aggregometry under standardised conditions. The cross-reactivity rates are: 7% (Orgaran), 89% (Fragmin), 83% (Clexane) and 86% (Fraxiparin). Although there are no controlled trials to determine the in viva cross-reactivity rates of LMW heparins and heparinoid, the low in vitro cross-reactivity rate of the latter favours its use in HIT. Nevertheless, the therapeutic use of these drugs in HIT should be preceded by exclusion of in vitro cross-reactivity. Heparin-induced thrombocytopenia (HIT) is a well-recognised complication of heparin therapy. Using pooled analysis Schmitt & Adelman estimated that the incidence of HIT is 1 .I % and 2.9% for porcine and bovine heparin respectively (1). Keywords: Heparin-induced thrombocytopenia, Platelet aggregation test, Cross-reactivity, Heparin, Low-molecular-weight heparins, Heparinoid. Correspondence to: Assoc Prof B. H. Chong, Department of Haematology, Prince of Wales Hospital, High Street, Randwick, N.S.W. 2031, Australia. Telephone 61 2 3829049, Fax 61 2 3984275. 525