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Resuspend in Tyrode's buffer with physiologic Ca++ (pH 7.4)

FIGURE 1 Schematic overview of washed platelet assays: HIT serum causes platelet activation at therapeutic (0.1-0.3 U/mL) heparin concentrations, but not in the presence of Fc receptor-blocking monoclonal antibody or high (100 U/mL) heparin concentrations. Platelet activation by HIT serum is potentiated by ADP release from platelet dense granules. Various platelet activation endpoints can be used. False-positive results can be avoided if typical reaction profiles of non-HIT platelet activation triggers are recognized: for example, (1) residual thrombin (activation at low but not high heparin concentrations, including activation in the presence of Fc receptor-blocking monoclonal antibody); (2) immune complexes (activation at low and high heparin concentrations, both of which are inhibited by Fc receptor-blocking monoclonal antibody); and (3) TTP serum (variable activation in the presence of heparin that is not inhibited by Fc receptor-blocking monoclonal antibody). Abbreviations: ACD, acid-citrate-dextrose; ADP, adenosine diphosphate; ATP, adenosine triphosphate; PRP, platelet-rich plasma; TTP, thrombotic thrombocytopenic purpura.

FIGURE 1 Schematic overview of washed platelet assays: HIT serum causes platelet activation at therapeutic (0.1-0.3 U/mL) heparin concentrations, but not in the presence of Fc receptor-blocking monoclonal antibody or high (100 U/mL) heparin concentrations. Platelet activation by HIT serum is potentiated by ADP release from platelet dense granules. Various platelet activation endpoints can be used. False-positive results can be avoided if typical reaction profiles of non-HIT platelet activation triggers are recognized: for example, (1) residual thrombin (activation at low but not high heparin concentrations, including activation in the presence of Fc receptor-blocking monoclonal antibody); (2) immune complexes (activation at low and high heparin concentrations, both of which are inhibited by Fc receptor-blocking monoclonal antibody); and (3) TTP serum (variable activation in the presence of heparin that is not inhibited by Fc receptor-blocking monoclonal antibody). Abbreviations: ACD, acid-citrate-dextrose; ADP, adenosine diphosphate; ATP, adenosine triphosphate; PRP, platelet-rich plasma; TTP, thrombotic thrombocytopenic purpura.

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