Irrespective of anaemia severity an Hb increase of 0 (-0.1; 0) g/dl was observed in patients with iron supplementation 1–5 days before surgery, 0.2 (-0.1; 0.5) g/dl in patients supplemented 6–10 days before surgery and 0.2 (-0.2; 1.1) g/dl in patients supplemented > 10 days before surgery (p < 0.001 for comparison 1–5 vs. 6–10 days) (Fig. 4). Here, GSTM1 is linked to anemia.