Patients with sickle cell disease (SCD) present with activated leukocytes at baseline that are suppressed after RBC transfusion. The relative median fluorescence intensity (rMFI) of monocyte CD63 (A), CD45 (B), neutrophil CD66b (C), and CD45 (D) were measured in the peripheral blood of HS (blue) and compared with those from patients with SCD, pretransfusion (red), and posttransfusion (green) (n = 7). For the posttransfusion samples, filled circles represent patients receiving full RBC exchange, empty circles represent patients receiving partial RBC exchange, and X represents patients in active crisis. Healthy vs SCD leukocytes pretransfusion comparison done using one-way ANOVA with Bonferroni post hoc. SCD leukocytes pre- vs posttransfusion comparison using a paired t test. The error bars represent standard deviation. ∗ P < .05; ∗∗ P < .01.