The importance of incorporating Ret-Hb into the diagnostic or screening panel of iron deficiency is due to the bioavailability of iron in the synthesis of hemoglobin in newly formed red blood cells (reticulocytes), because Ret-Hb levels are not as influenced by other conditions (e.g., inflammation) as those of acute phase reactants such as ferritin and transferrin [28], or the fluctuations caused by the diurnal variation and/or the quality of food intake, unlike serum iron [29,30]. This evidence concerns the gene GSTM1 and nutritional disorder.