The hemoglobin A1c blood test, also referred to as Hb1Ac, measures a diabetic's average blood sugar level for the past 2 to 3 months, states WebMD. The result indicates how effectively diabetes is controlled over time.
Hemoglobin is a component of the blood that supplies the body with vital oxygen. Increased intake of sugar in diabetics leads to accumulation of blood glucose, which binds with hemoglobin. A hemoglobin A1c blood test determines the average amount of glycated, or sugar-coated, hemoglobin.
Excessive blood sugar levels signify elevated concentrations of glycated hemoglobin, which result in higher Hb1Ac readings, notes WebMD. The data from an Hb1Ac test also serves as the basis in making changes to a diabetic's blood sugar control plan to ensure that blood glucose levels remain within a healthy target range.