Comparison of cPRP Versus Washed Platelet Assays

Sensitive washed platelet assays generally show almost 100% cross-reactivity of HIT antibodies for LMWH (Greinacher et al., 1992; Warkentin et al., 1995a). Indeed, UFH and LMWH are essentially indistinguishable in these assays. However, very different results have been reported by investigators using c-PRP assays (Makhoul et al., 1986; Chong et al., 1989; Kikta et al., 1993; Vun et al., 1996). Here, LMWH consistently shows less cross-reactivity compared with UFH. It is possible that differences in nonidiosyncratic heparin-induced platelet activation underlie these observations (see Chapter 4): UFH is more likely to result in weak platelet activation, including some PF4 release, which leads to amplification of the platelet activation response in the presence of PF4-H-reactive HIT antibodies. In contrast, in washed platelet assays, IgG-mediated platelet activation, but not nonidiosyncratic HIPA, occurs.

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