Kynurenine is a marker of osmotic fragility of stored RBCs and is affected by donor age, BMI, and sex. Machine-learning approaches were used to determine metabolic predictors of osmotic fragility of stored RBCs. Results identified kynurenine as the top predictor (A), which was confirmed via a Spearman correlation analyses (B). (C) Scatterplot of osmotic fragility vs kynurenine: x-axis and y-axis, respectively. (D-I) Volcano plots, scatter plots, or box and whisker plots showing the strong positive association between kynurenine levels and donor age, sex, and BMI. AC, acyl-carnitine; AU, arbitrary unit.