Distribution of aggregation response to increasing epinephrine concentrations among healthy individuals. These histograms depict the number of subjects (y-axis) with a given level of platelet aggregation (x-axis) to no agonist (A) and epinephrine at concentrations of 0.4 μM (B), 1.5 μM (C), and 10 μM (D). Panel D shows fewer subjects because specimens were not tested at higher concentrations if more than 60% aggregation was observed at lower concentrations.