GSTM1 and anemia (phenotype): Using a linear regression analysis with fixed effects, we found that CRP level (p < 0.001), transfused RBC units (p < 0.001) and moderate anaemia (p = 0.04) were predictors for prolonged LOS but not gender, BMI, ID, iron supplementation, preoperative Hb increase, mild or severe anaemia (Supplemental Fig. 9).