A preoperative Hb level ≤ 10 mg/dL (odds ratio [OR], 20.1; 95% confidence interval [CI], 4.71–125, p < 0.001) and transferrin saturation (TSAT) < 25% (OR, 12.8; 95% CI, 2.51–129, p < 0.001) were predictors for anemia improvement. This evidence concerns the gene GSTM1 and anemia (phenotype).