Iron supplementation resulted in a preoperative increase in median Hb levels of 0 (-0.3; 0) g/dl in patients with mild (n = 85), 0 (0; 0.4) g/dl in patients with moderate (n = 51), and 0.1 (0; 0.8) g/d in patients with severe (n = 20) anaemia (p < 0.001 for comparison mild vs. severe) (Fig. 3). This evidence concerns the gene GSTM1 and anemia (phenotype).