Glycated hemoglobin (HbA1c or A1c) provides a measure of average blood glucose levels over the past 2-3 months and is used to diagnose and monitor diabetes. However, A1c levels can be affected by factors like anemia, kidney disease, pregnancy, blood transfusions, and hemoglobin variants. Alternative markers like fructosamine and glycated albumin may be more accurate than A1c in some conditions, but lack standardization. The document discusses the uses and limitations of A1c testing as well as conditions that can impact interpretation and alternative options for assessing glycemic control.