Platelet aggregation in “aa” and “bb” donors. Platelet aggregation in subjects homozygous for “aa” (▪) or “bb” (▴) was induced by CRP-XL, and the extent of aggregation (A) as well as the maximum rate of aggregation (C) is shown with respect to dose. Samples from the same subjects were also treated with ADP, and the extent of aggregation (B) and maximum rate (D) are also shown. Data are expressed as the mean ± SEM, and statistically significant differences between the “aa” and the “bb” groups (Mann-Whitney U test, P < .05) are marked by an asterisk.