EPO and anemia (phenotype): Hemoglobin A1c is useful, yet limitations persist, notably intra-subject variability even with National Glycohemoglobin Standardization Program (NGSP)-certified methods in obese youth [62] and reduced reliability in conditions with altered red-cell turnover such as hemoglobinopathies, anemia, pregnancy, recent blood loss or transfusion, hemolysis, and erythropoietin use [63].