ABSTRACT

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 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. 12).