RBC S1P decreases during storage and is higher in packed RBCs from female and older donors. (A) An overview of the REDS-IV RBC Omics program is provided in panel A. (B-C) As part of the recalled donor arm of the study, 1929 units from 643 extreme hemolyzing donors were tested for RBC S1P levels (AUs, which were found to decrease during storage (B), and were lower early on during storage in AS-3 packed RBC units (AU) (C). (D-E) Higher levels of S1P were observed in blood donated by female donors (box and whisker plot; median ± ranges[D]), older donors (volcano plot of metabolic correlates to age across all blood donors tested in this study; x-axis indicates log2-fold changes per unit of age for each metabolite and the y-axis indicates the negative log10 of q-values for such correlations [E]), independent storage duration and additive. Asterisks indicate significance (ANOVA with multiple column comparisons; ∗∗P < .01, ∗∗∗P < .001, ∗∗∗∗P < .0001). AU, arbitrary unit.