Hemoglobin A1C (HbA1c) test: what it means
What it measures
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.
Why it’s ordered
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.
General reference range
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.
If it’s high
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.
If it’s low
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.
A result is not a diagnosis
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.
Medicines that can move this result
Steroids make the liver release more glucose and blunt insulin's effect, so blood sugar runs higher for as long as the course lasts. Because A1c averages roughly three months, a short course can send glucose up sharply while barely moving the A1c, and a long course moves both.
Source ↗Thiazide water pills reduce insulin release and increase insulin resistance, nudging blood sugar up enough that the label warns diabetes which was previously borderline can become apparent during treatment.
Source ↗Statins slightly worsen how the body handles sugar, and the FDA label records reported increases in both A1c and fasting glucose. The label does not give a size for the rise, and a statin is prescribed to lower cardiovascular risk, so this is a question for the prescriber rather than a reason to stop.
Source ↗This antipsychotic drives weight gain and insulin resistance, and the label carries a warning that blood sugar can rise sharply rather than gradually, in some cases to a medical emergency.
Source ↗This transplant anti-rejection drug impairs insulin secretion from the pancreas, so blood sugar and A1c climb. The label states it has been shown to cause new diabetes after kidney, liver, heart and lung transplantation.
Source ↗At the gram doses used for cholesterol, not the milligrams in a multivitamin, niacin worsens glucose tolerance and pushes fasting glucose, and with it A1c, upward. The label asks for close observation of diabetic patients, particularly in the first months and after any dose change.
Source ↗It makes the marrow pump out a wave of brand-new red cells that have had little time to pick up sugar, so the A1c reads lower than your actual glucose control. Erythropoietin administration is listed among the causes of a falsely low A1c.
Source ↗Starting iron for iron-deficiency anemia replaces old, long-circulating red cells with young ones, so A1c falls for a few months without your blood sugar having actually improved. Iron supplementation is listed among the causes of a falsely low A1c.
Source ↗Do not stop a prescribed medicine over a lab number. These are recognised associations, not a finding about your result — your value may have nothing to do with any medicine you take, and the list is not complete. Bring it to whoever prescribed the drug; they can weigh it against why you are taking it.
Frequently asked
- What does the Hemoglobin A1C (HbA1c) test measure?
- 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.
- What is a normal Hemoglobin A1C (HbA1c) test range?
- 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.
- What does a high result mean?
- 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.
- What does a low result mean?
- 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.
Other lab tests
Sources
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.