In our study, 48.1 % of patients [95 % confidence interval (CI) 45.2–58.6] showed anaemia (31 % symptomatic): 42.0 % mild (10 ≤ Hb ≤ 11.9 g/dL), 5.6 % moderate (8 ≤ Hb ≤ 9.9 g/dL), and 0.5 % severe (Hb <  8 g/dL). This evidence concerns the gene GSTM1 and anemia.