Heparin-induced thrombocytopenia--association with a platelet aggregating factor and cross-sensitivity to bovine and porcine heparin.

Heparin-induced thrombocytopenia is an infrequently suspected adverse drug reaction since its sequelae often mimic the underlying condition for which the drug is being used. A concomitant decline in platelet count and increase in heparin requirements should alert the clinician to the possible presence of this disorder. A 36-year-old black male developed severe thrombocytopenia with thrombosis while being treated with porcine intestinal mucosal heparin. Platelet counts returned to near-normal levels upon discontinuation of heparin, but quickly dropped again upon resuming treatment with bovine lung heparin. The patient subsequently was treated with warfarin and dipyridamole, with no further complications. Treatment of delayed-onset severe heparin-induced thrombocytopenia consists of stopping the heparin and substituting antiplatelet agents and oral anticoagulants when continued inhibition of coagulation is required.