HbA1c values used for diagnosing and treating diabetes can be affected by factors such as red blood cell lifespan, hemolysis, red cell transfusion, and the presence of minor Hb species like HbA2 and HBF in hemoglobinopathies like sickle cell disease, homozygous HbC disease, HbSC disease, and β-thalassemia. This evidence concerns the gene GSTM1 and diabetes mellitus.