What is an A1C?

Dr. James Grant

| 3 min read

James D. Grant, M.D. is senior vice president and chief...

One of the most commonly used tests to screen for diabetes and prediabetes – as well as for tracking how well people with the conditions are managing their blood sugar – is the A1C test.
The A1C test is also known as the hemoglobin A1C or HbA1c test. It’s a simple blood test that measures your average blood sugar levels during the past three months. Some like to compare the A1C test to a baseball player’s season batting average: it tells you about a person’s overall success managing their blood sugar.

What do A1C levels show?

The A1C test measures the percentage of your red blood cells that have sugar-coated hemoglobin. The higher your blood sugars levels are, the higher the A1C number is. As blood sugar levels improve, the A1C level will come down. Everyone has some sugar attached to hemoglobin on their red blood cells. The higher the percentage of your blood cells with sugar attached to them, the more at risk you are for prediabetes or diabetes complications.
DiagnosisA1C Level
NormalBelow 5.7%
Prediabetes5.7% to 6.4%
Diabetes6.5% or above
The USPSTF recommends screening adults aged 35 to 70 who have overweight or obesity for prediabetes and type 2 diabetes using a fasting plasma glucose, the A1C test, or an oral glucose tolerance test. Talk to your health care provider to understand your risks for diabetes and if you should have a screening blood test.

Managing diabetes

For most people living with diabetes, generally the goal is to keep their A1C level to 7% or less. A health care provider may set an individualized goal that fits your personal health needs, including your age and any other medical conditions you may be managing.

How often is A1C measured?

For people with a diagnosis of diabetes, itis common for health care providers to order an A1C test at least twice a year. If your blood sugars tend to fluctuate or your previous A1C is above goal, your health care provider may order an A1C test more frequently than every three months.

Understanding A1C and eAG 

While the A1C test can tell individuals with prediabetes and diabetes how they are doing over a two-to-three-month period, it’s hard to compare A1C levels to the everyday readings individuals with diabetes see when they are self-monitoring their blood sugar levels using their meters or continuous glucose monitors. That’s because A1C levels are reported as a percentage, and glucose monitors use units like mg/dL or mmol/L.
There’s another measurement called estimated average glucose, or eAG. eAG is a figure calculated from your A1C level that is reported in mg/dL, or mmol/L. This is simpler to understand for people with diabetes who are tracking their blood sugar levels at home, as it uses the same units of measurement as glucose monitors.
Understanding your eAG can help relate daily blood sugar levels with the overall progress you are making with any medications, diet and lifestyle changes through your treatment plan.
The American Diabetes Association has an online conversion calculator for A1C to eAG:
The A1C test is the primary test to monitor a person’s journey with diabetes. Having your A1C done at the lab does not replace the blood sugar monitoring people with diabetes must do at home. As blood sugar changes during the day, be sure to keep track of your highs and lows. Track your symptoms and share your results with your doctor to make sure your treatment plan is meeting your needs.
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