CAN LOW-MOLECULAR-WEIGHT HEPARINS AND HEPARINOIDS BE SAFELY GIVEN TO PATIENTS WITH HEPARIN-INDUCED THROMBOCYTOPENIA SYNDROME

Background. Low molecular weight heparin (LMWH) and heparinoids have b een offered as alternatives to unfractionated heparin (UH) to patients with heparin-associated antiplatelet antibodies (HAAb) and heparin-in duced thrombocytopenia syndrome (HIT). Some of these patients have had continued HIT in the presence of the UH substitutes. It would seem im portant to know whether the heparin substitute is likely to cause pati ents' platelets to aggregate before administering the substitute to pa tients with HAAb. Methods. Patients with HIT were identified as having HAAb by positive platelet aggregometry testing with commercial UH. Pl asmas from 51 patients with HAAb were tested for the ability to aggreg ate platelets in the presence of two LMWHs (Mono-Embolex NM and Fragmi n) and one heparinoid (Org 10172). Results. The proportions of plasmas reacting to each UH substitute are Mono-Embolex NM, 60.8%; Fragmin, 2 5.5%; and Org 10172, 19.6%. Although Fragmin and Org 10172 aggregated platelets in the presence of HAAb significantly less often than Mono-E mbolex NM (p < 0.001), a patient with HAAb has a substantial chance of reacting to one of these UH substitutes. Conclusions. Before giving a LMWH or heparinoid to a patient with HAAb, one should determine with in vitro testing that the patient's HAAb will not cause platelet aggre gation in the presence of the heparin substitute.