Other Assays Using Citrated Anticoagulated Whole Blood or PRP

Tomer (1997) reported a c-PRP activation assay for HIT antibodies in which the activation endpoint is quantitation of binding of fluorescein-labeled recombinant annexin V to platelets, as detected using flow cytometry. Annexin V, a placental protein, interacts with the prothrombinase-binding anionic phospholipids expressed on the surface of activated platelets and correlates with platelet procoagulant activity. It is uncertain whether the reaction conditions employed (e.g., 30-min incubation at 26° C) or the high sensitivity of annexin V binding (300-fold increase over baseline) overcomes the inherent limitations of sensitivity observed with other assays using c-PRP. Gobbi and colleagues (2003) developed a flow cytometry assay modeled after that of Tomer (1997), except that loss of serotonin from platelet granules was used as the platelet activation endpoint. Vitale et al. (2001) found P-selectin to be a better marker of platelet activation than annexin V.

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