Posttransfusion and in vivo platelet (PLT) function in healthy humans. (A) Time course of the healthy human crossover study, including baseline (BL) PLT test; PLT function 24 hours after loading dose (LD) with 325 mg of ASA and 600 mg of clopidogrel; and 1-, 4-, and 24-hour PLT function tests posttransfusion. (B) Absolute PLT counts at different time points of the study from individuals during RT-stored PLT transfusion round (red circles) and 4°C-stored PLT transfusion round (blue squares; n = 7-8; shown as mean ± standard error of the mean [SEM]). (C) Corrected count increments at posttransfusion time points (n = 7-8; shown as mean ± SEM). (D) PLTs were washed before assessment by light transmission aggregometry. Platelets were stimulated with 20 μg/mL of collagen, 20 mM of ADP, and 0.5 mM of arachidonic acid (n = 7-8; shown as mean ± SEM of maximum aggregation). (E) PLT reactivity tested by Verify NOW for ASA (aspirin reaction units [ARUs]; n = 7-8; shown as mean ± SEM). (F) Individual responses of participants to autologous transfusion, after LD (normalized to 0) and at 1, 4, and 24 hours posttransfusion (shown as percentage change from bleeding LD value; negative values indicate shortening of bleeding time [BT; ie, correction of prolonged BT], and positive values indicate prolongation of bleeding time [ie, worsening of prolonged BT]). Responses after transfusion of cold-stored autologous units (4°C stored; n = 8; left), and responses after transfusion of RT-stored autologous units (RT stored; n = 7; right). *P = .0110 (4-hour time point) and P = .0154 (24-hour time point) (B) and P = .015 (4-hour time point) and P = .0098 (24-hour time point) (C), **P = .0088 (D) and P = .0018 (E). CCI, corrected count increment; ns, not significant.