We have started a clinical trial with the objective of comparing the effectiveness of 1000 mg of ferric carboxymaltose with fractionated iron sucrose 200 g/48 h for the treatment of postoperative anaemia, by measuring the change of haemoglobin (Hb) levels from postoperative day (POD) 1 to POD 30. The gene discussed is GSTM1; the disease is anemia (phenotype).