Flow cytometric analysis of platelets activated with HIT sera, thrombin, and calcium ionophore.

Platelets (p) and microparticles (mp) were identified using fluorescence (FL1, FITC anti-GPIbα) (y-axis) and size (FSC) (x-axis) characteristics. Control platelets included; (A) platelets incubated in buffer alone; (B) platelets incubated with patient serum, which tested negative for HIT, in the presence of 0.1 U/ml heparin; and (C) platelets incubated with HIT serum with no heparin added. (D) Platelets were incubated with HIT serum in the presence of 0.1 U/ml heparin. (E) As a positive control, platelets were also incubated with 1 U/mL thrombin or (D) 10 μm calcium ionophore A23187. Microparticles (MP) were generated with heparin-induced thrombocytopenia serum, thrombin, and calcium ionophore and not with the control serum. The percent of microparticles (the percent of fluorescent events in the microparticle gate) generated by HIT serum was 40%; thrombin, 45%; and calcium ionophore, 47%. The results of a representative experiment are shown.