The hemoglobin A1C (HbA1c) test is a blood test that measures the percentage of your red blood cells that have glucose (sugar) attached to their hemoglobin, the protein that carries oxygen. Because glucose stays attached over the life of a red blood cell, the result reflects your average blood glucose over the past two to three months rather than a single moment. It uses one blood sample, and no fasting is required.
A clinician may use an A1C test to help screen for or diagnose prediabetes and type 2 diabetes. In people who already have diabetes, it is commonly used to help monitor how well blood glucose has been controlled over time.
As a general guide (given as a percentage), commonly cited categories are: normal — below 5.7%; prediabetes — 5.7% to 6.4%; diabetes — 6.5% or higher. For many people already living with diabetes, a common management goal is to keep the level below 7%, though individual targets differ. Important: these categories are only a general guide. Normal value ranges can vary slightly among different laboratories and may also depend on your age, sex, health, and the testing method used. The reference range printed on your own lab report is what applies to you, and a number on its own is not a diagnosis — talk with your provider about the meaning of your specific results.
A higher A1C generally reflects a higher average blood glucose level over the preceding weeks to months and can be seen with prediabetes or diabetes. Persistently high levels may be associated over time with a higher risk of health problems such as heart disease, stroke, kidney disease, nerve damage, and eye disease. Certain conditions — such as anemia or other blood disorders, kidney failure, and liver disease — as well as some medications can also affect the accuracy of A1C results. This is a general association, not a complete list and not a diagnosis.
MedlinePlus does not describe a "low" A1C result or use the A1C test to identify low blood sugar, so it is generally not reported or interpreted as "low" in the way high values are. If your result is below the typical range, that is something to discuss with your clinician in the context of your overall health. Your clinician interprets your A1C alongside your medical history, other tests, and individual circumstances. This is general information, not medical advice, and it is not a substitute for a qualified healthcare provider's interpretation of your own results.
Reference ranges vary by laboratory, age, sex, and method — the range on your own report is what applies to you. A single value out of range doesn’t confirm any condition; your clinician interprets it alongside your symptoms, history, and other results. This page is general information, not medical advice.
General reference, not medical advice, and not a substitute for your clinician. Lab reference ranges and interpretation depend on the laboratory and on your individual situation — discuss your results with a licensed healthcare professional.