ABSTRACT
INTRODUCTION Heparin-induced thrombocytopenia (HIT) is a distinct clinicopathologic syndrome caused by platelet-activating antibodies that recognize complexes of platelet factor 4/heparin (PF4/H). Its strong association with venous and arterial thrombosis represents a striking paradox. However, thrombocytopenia itself is common in clinical medicine. Furthermore, heparin is usually given to patients who either have thrombosis, or who are judged to be at a high risk for thrombosis. Thus, thrombocytopenia with or without thrombosis during heparin treatment does not necessarily indicate a diagnosis of HIT. Indeed, several disorders can closely resemble HIT (see chap. 3).
