Sera from 13 patient sera were analyzed using flow cytometry and MAIPA to determine their antiplatelet activity. AB sera, isotype-matched IgG, and patient sera in the absence of quinine were used as negative controls. All control samples gave rise to negative results. The strength of reaction in flow cytometry experiments was scored on the basis of the shift of the geometric mean of fluorescence (GMF) compared with negative controls (half a log fluorescence was scored as (+), and the highest score (++++) was given to samples given rise to a shift of 2 log fluorescence or more). In the MAIPA assay a positive result was defined as absorbance beyond the mean + 3 SD of 50 normal samples (ie, 0.1). The positive results were scored from weak (+) (0.1-0.3), ++ (0.3-0.8), +++ (0.8-1.5), to strong (++++) (> 1.5). — indicates negative reaction.