Different mechanisms of platelet preactivation in neonates and adults. Characteristics of preterm neonates <32 weeks GA, 32 to 36 weeks GA, >36 weeks GA (t), infants 28d-2a, children 2 to 13a and adults >13a are displayed. (A) CD62P, (B) CD63 expression, and (C) GPIIb/IIIa activation were assessed by flow cytometry on resting platelets in whole blood. (D,E) Quadrant analysis of CD63 and PAC-1 was performed. (F-H) Automated clustering analysis of resting platelets. (G) Heat map of platelet subpopulations. Representative curves are shown in panels D and F. The median ± 95% confidence interval (CI) values are displayed in panels A-C. The mean ± 95% CI is shown in panels E and H. Differences were analyzed using the Kruskal-Wallis test. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001. ns, nonsignificant.