Hemoglobin A1c (HbA1c) is a blood test that measures a person's average blood sugar levels over the past three months. It's also known as the glycated hemoglobin test.  HbA1c test What it measures The percentage of red blood cells that have glucose-coated hemoglobin How it works Glucose in the blood sticks to hemoglobin, a protein in red blood cells. The amount of HbA1c formed is directly related to the amount of glucose in your blood. What it's used for Diagnosing type 2 diabetes and monitoring blood glucose control in people with diabetes How it's performed A blood sample is taken through a needle from a vein in a lab or at home A high HbA1c means you have too much sugar in your blood and are more likely to develop diabetes complications. The 2022 ADA guidelines recommend that HbA1c should be maintained below 7.0% for most patients.  Factors that can affect the accuracy of your HbA1c test results include: Alcohol use disorder Blood transfusion Chronic kidney failure Bleeding Being pregnant Cirrhosis of the liver Sickle cell anemia and hemolytic anemia High-altitude living Taking an iron supplement