Fatal heparin-induced thrombocytopenia 8 months after prior exposure to heparin.

r l T o t t d w p m EPARIN-INDUCED THROMBOCYTOPENIA (HIT) is a syndrome of thrombocytopenia caused by circulating Ig ntibodies (“HIT antibodies”) that bind to heparin platelet actor 4 complexes.1 HIT with thrombosis (HITT) is HIT with he clinical syndrome of arterial or venous thrombosis because f platelet activation. The frequency of development of HIT ntibodies depends on the type of heparin exposure (higher with nfractionated heparin [UFH] compared with low–moleculareight heparin [LMWH]) and the patient population (surgical atients higher than medical patients). Cardiac surgical patients ho are exposed to UFH perioperatively have a 50% incidence f detectable HIT antibodies.1 In orthopedic surgical patients, he incidence is 15% with exposure to UFH but only 8% with xposure to LMWH.1 Not all patients who develop HIT antiodies will become thrombocytopenic. Clinical HIT with hrombocytopenia below 100,000/ L is uncommon, and hrombosis (HITT) is rare (0%-5% of patients).2-5 Thrombocytopenia develops generally within 4 to 15 days of xposure to heparin but occasionally can occur within hours rapid-onset HIT) because of the presence of circulating HIT ntibodies formed after a recent exposure.6-8 Of 73 patients dentified to have had rapid-onset HIT over a period of 15 ears, most had received heparin (all UFH) within the previous weeks and all within the previous 100 days.6 The authors describe a case of fatal rapid-onset HIT in a patient f previously unknown HIT status who had received UFH more han 1 year and LMWH 8 months before the current admission.