Hemoglobin A1C (HbA1c) Test
The A1C test measures your average blood glucose levels over the past two to three months, serving as a key tool for diagnosing and monitoring diabetes and prediabetes.
What is a hemoglobin A1C (HbA1C) test?
The A1C test is a blood test that shows your average blood sugar (glucose) level over the past two to three months. Glucose in your blood sticks to hemoglobin, a protein in your red blood cells. Because red blood cells live for about three months, the test measures the percentage of your red blood cells that have glucose-coated hemoglobin.
What is it used for?
Unlike home glucose tests that measure your sugar level at a single moment, the A1C test provides a long-term average. It is used to:
- Screen for or diagnose: Type 2 diabetes and prediabetes.
- Monitor: How well you are controlling your blood glucose levels if you have already been diagnosed with diabetes or prediabetes.
Note: The A1C test is not used to diagnose type 1 diabetes, though it may be used to monitor it.
Why do I need an A1C test?
The CDC recommends testing if you are over age 45. If you are under 45, you should be tested if you have risk factors such as being overweight, having a family history of diabetes, high blood pressure, high cholesterol, or a history of gestational diabetes. You may also need the test if you experience symptoms of diabetes, such as:
- Increased thirst or hunger
- Frequent urination
- Unexplained weight loss
- Blurred vision
- Numbness or tingling in hands or feet
- Fatigue or slow-healing sores
What happens during the test?
A health care professional will collect a blood sample from a vein in your arm using a small needle. The process typically takes less than five minutes.
Preparation and Risks
Tell your provider about all medicines you take, as some (such as opioids or HIV medications) may affect results. Do not stop taking medications unless instructed. Let your provider know if you are pregnant. There is very little risk to the test, with only a slight chance of minor pain or bruising at the needle site.
What do the results mean?
Results are reported as a percentage. Common diagnostic ranges include:
- Normal: Below 5.7%
- Prediabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
If your results are high, your provider may order follow-up tests, such as a fasting blood glucose test or an oral glucose tolerance test (OGTT), to confirm a diagnosis.
Important Considerations
The A1C test is not used to diagnose gestational diabetes. Additionally, conditions that affect red blood cells—such as anemia, blood disorders, kidney failure, or liver disease—can make A1C results inaccurate. In these cases, your provider may recommend alternative testing methods.