The reference intervals differ by age and gender: The Hb cut-off for definition of anemia decreases from 135 g/L at 0–1 weeks of age to 90 g/L at 2 months and then increases to 105 g/L at 4–24 months, 110 g/L at 2–5 years and 115 g/L at 6–11 years. This evidence concerns the gene GSTM1 and anemia.