Platelet activation in control participants and in patients with SCD at steady state and during VOC. Each dot represents the percentage of activated platelets from an individual patient with SCD or control participant, as determined by flow cytometry detection of platelet cell-surface (A) activated fibrinogen receptors and (B) P-selectin. Significant P values are indicated as determined by unpaired t test. P-selectin values were analyzed by the Mann-Whitney test because these results were not normally distributed. Boxes indicate median and interquartile ranges, and whiskers indicate ranges.