ABSTRACT
Heparin-induced thrombocytopenia (HIT) is a unique immune-mediated disorder. HIT is common, occurring in as many as 5% of certain patient populations. Affected patients often develop the paradox of thrombosis, but not bleeding, despite having thrombocytopenia. One possible reason for this unique clinical profile is the central role of the platelet Fc,,! receptor (Fc,,!R) Ila in mediating platelet activation in HIT. Indirect evidence suggesting a crucial role for platelet activation in the pathogenesis of HIT is the observation that thrombocytopenia caused by HIT antibodies is strongly associated with thrombosis, whereas formation of HIT antibodies without thrombocytopenia is not (Warkentin et aI., 1995).
