How does the hemoglobin A1C test work?
The hemoglobin A1C is a test that measures your average blood sugar for the past three months. If your hemoglobin A1C is high it could mean that you are prediabetic or diabetic.
If you have diabetes, your doctor may use the A1C to check how well you are controlling your blood sugar. A high hemoglobin A1C may mean that your treatment plan needs revision. The A1C is also used to diagnose diabetes or prediabetes.
Hemoglobin is the protein that gives red blood cells their color. Its job is to carry oxygen to all the cells in your body. As red blood cells travel around the body, glucose in the bloodstream attaches itself to the hemoglobin. The A1C test measures how much glucose is attached. Since red blood cells live around three months, the A1C test shows how high your blood sugar has been for the past three months.
A1C as a screening test
Combined with other indicators, the A1C can screen for both type 1 and type 2 diabetes. Type 1 diabetes usually develops during childhood or young adulthood. No one is certain what causes it. Type 2 usually develops later and has certain risk factors. You are more likely to develop type 2 diabetes if you:
- Are over 45 years of age
- Are overweight
- Lead a sedentary lifestyle
- Have a parent or sibling with diabetes
- Had diabetes during pregnancy or had a baby weighing over 9 pounds
If you are being screened for diabetes, your A1C results will fall into one of three categories:
- Less than 5.7%: normal, not diabetic
- 5.7% to 6.4%: prediabetic
- 6.5% or higher: diabetic
A1C as a monitoring test
If you have already been diagnosed with diabetes, your doctor may use the hemoglobin A1C test to monitor your blood glucose levels. A result of 7% or less usually means that you are controlling your diabetes.
Although less than 7% is a common goal, a higher reading may be better for some people. If you are prone to low blood sugar, also known as hypoglycemia, your doctor may prefer an A1C between 7% and 8%. A higher goal may also be better for those who have had diabetes for a long time or who have complications of the disease.
Difference between A1C and blood glucose
If you have diabetes, you may check your blood sugar at home. This test differs from the A1C. When you test your blood glucose, you are checking your blood sugar level at one moment in time. Your test result will reflect how long it has been since you ate something and the type of food you ate.
Home glucose testing gives you and your doctor information that the A1C does not. The A1C gives a blood sugar average but does not show whether your levels are steady or whether they go very high and very low. Your doctor needs both types of tests to understand how well you are controlling your blood sugar.
How accurate is the A1C?
Your doctor can do an A1C test using a blood sample from a finger prick. Called a point-of-care test, this test can be processed quickly. Your doctor may instead choose to take a larger blood sample and send it to a lab for processing. The results of the lab test may be slightly more accurate.
If you have recently had a blood transfusion, your A1C may not be accurate. Other health conditions can affect the red blood cells and result in inaccurate A1C results. These include:
Why the A1C is important
If you have diabetes, a high hemoglobin A1C means that you are more likely to experience complications. Some complications are serious. They include:
Screening for diabetes is also important. Those with an A1C greater than 6% are at high risk of developing diabetes in the next 5 years. Identifying them is critical. Research shows that two interventions can lower their chances of developing diabetes. Lifestyle changes can reduce their risk by 50%. Using the drug metformin can reduce it by 30%.
What to do about a high A1C
After a high hemoglobin A1C, you and your doctor can work together to lower your numbers and reduce your risks. Your doctor may recommend a three-pronged approach combining education, diet, and exercise. Also, you may need to lose weight if you are overweight.
Medically Reviewed on 1/7/2022
Centers for Disease Control and Prevention: “All About Your A1C,” “Diabetes Risk Factors.”
Diabetes Care: “A1C Level and Future Risk of Diabetes: A Systematic Review.”
Eyth, E., Naik, R. StatPearls, “Hemoglobin A1C,” StatPearls Publishing, 2021.
Merck Manual Consumer Version: “Diabetes Mellitus (DM).”
Mount Sinai Hospital: “A1C test.”
National Institute of Diabetes and Digestive and Kidney Diseases: “The A1C Test & Diabetes.”
University of California San Francisco: “A1C Test.”