The measurement of HbA1c to monitor glycemic control in diabetic patients with homozygous Hb S has limited value and should be interpreted with caution, as factors such as anemia, decreased red cell survival causing decreased glycated hemoglobin values, increased Hb F, and transfusion requirements may affect the HbA1c results.[11, 13] Alternative methods such as fructosamine, glycated serum protein or self-monitoring of blood glucose should be considered in patients with homozygous Hb S. The gene discussed is GSTM1; the disease is anemia (phenotype).