A1c is a test that shows the average level of blood sugar over the past 2 to 3 months. People who have diabetes usually have this test to see whether their blood sugar levels have been staying within a target range. This test is also used to diagnose diabetes. This test may not be appropriate for everyone because many things can affect the life span of red blood cells, such as the second or third trimester of pregnancy, a recent blood loss or a blood transfusion, sickle cell disease, hemodialysis, or erythropoietin (ESA) medicine.
A1c test results show your average blood sugar level over time. The result is reported as a percentage. Your goal is to keep your hemoglobin A1c level as close to your target level as possible. You and your doctor will work together to set your safe target level.
The result of your A1c test can also be used to estimate your average blood sugar level. This is called your estimated average glucose, or eAG. Your eAG and A1c show the same thing in two different ways. They both help you know about your average blood sugar over the past 2 to 3 months.
The table below shows A1c with estimated average glucose.
A1c and estimated average glucose (eAG) footnote 1
Hemoglobin A1c %
Estimated average glucose (mg/dL)
American Diabetes Association (2019). Standards of medical care in diabetes—2019. Diabetes Care, 42(Suppl 1): S1–S193. Accessed December 17, 2018.
Current as of: December 19, 2019
Author: Healthwise Staff Medical Review: E. Gregory Thompson MD - Internal Medicine Kathleen Romito MD - Family Medicine Rhonda O'Brien MS, RD, CDE - Certified Diabetes Educator
Medical Review:E. Gregory Thompson MD - Internal Medicine & Kathleen Romito MD - Family Medicine & Rhonda O'Brien MS, RD, CDE - Certified Diabetes Educator
American Diabetes Association (2019). Standards of medical care in diabetes-2019. Diabetes Care, 42(Suppl 1): S1-S193. Accessed December 17, 2018.