Hb was categorized as normal (Hb ≥ 11 g/dL), mild anaemia (Hb 10.0–10.9 g/dL), moderate anaemia (Hb 7.0–9.9 g/dL), or severe anaemia (Hb < 7.0 g/dL). This evidence concerns the gene GSTM1 and anemia.