Technically speaking…

The A1C test measures the amount of glycated hemoglobin in the blood, which indicates average blood glucose levels over the preceding 2 to 3 months. Also called glycated hemoglobin or glycohemoglobin, the A1C test is based on the addition of glucose to hemoglobin over the typical 120-day life span of a red blood cell. Formation of glycated proteins is proportional to the concentration of glucose in the blood. The A1C test helps gauge risk of long-term complications; studies have demonstrated substantial reductions in long-term complications of diabetes with lowering of A1C.