GSTM1 and anemia (phenotype): In the absence of inflammation, serum ferritin is widely agreed to be the most specific non-invasive biochemical test to diagnose iron deficiency and is an accurate reflection of total body iron stores.19 Assaying ferritin levels is useful because a reduction in this marker occurs before detectable reductions in Hb, serum iron levels or erythrocyte size, which traditionally indicate the presence of anaemia at more severe stages of iron deficiency.