On-target blood glucose control helps you feel your best and prevent or delay complications. The best measure of long-term average blood glucose control is a simple laboratory test called the A1C.
What is A1C? An A1C (pronounced A-one-C) test reflects your average blood sugar or glucose level over the past two to three months. When you check your blood sugar with a meter after fasting and before or after meals, you won’t capture all the ups and downs. The A1C, also known as a glycosylated hemoglobin test or HbA1c, offers you an overview to compare with your blood sugar checks. The test requires a small blood sample—no fasting is necessary—for a lab analysis.
How does it work? The test measures glycosylated hemoglobin, or the percentage of hemoglobin molecules in your red blood cells with glucose attached to them. (Hemoglobin is a protein in red blood cells that carries oxygen.) Glucose naturally sticks, or “glycosylates,” to some of the hemoglobin in red blood cells. When blood glucose is high, more hemoglobin molecules have glucose attached to them. The glucose stays there for the life of the red blood cell (about 120 days), which is why the test covers a three-month period.
What are “good” A1C levels? For people without diabetes, about 4 to 6 percent of hemoglobin is glycosylated, so an A1C of 4 to 6 percent is considered normal. An A1C that’s 6.5 percent or higher is sufficient for the diagnosis of diabetes, according to the American Diabetes Association (ADA). The ADA states that an A1C 5.7 to 6.4 percent is diagnostic for prediabetes. For people with diabetes, maintaining an A1C of less than 7 percent over time can reduce the risk of the heart, eye, kidney and nerve damage associated with having diabetes for many years. Talk to your doctor about what your A1C target should be.
How often to get tested? The ADA recommends an A1C test at least twice a year if your blood glucose control is stable and within target. You may want to have the test more frequently (such as every three months) in some situations, such as during adjustment of your diabetes treatment, if you are considering pregnancy or during insulin therapy.
How does A1C relate to regular blood sugar checks? Estimated average blood glucose (eAG) is your A1C results translated into the same units (milligrams per deciliter) that you get when you use your blood glucose meter. Here’s how it stacks up:
If your A1C is 5 percent, your eAG is 97 mg/dL.
If your A1C is 5.5 percent, your eAG is 111 mg/dL.
If your A1C is 6 percent, your eAG is 126 mg/dL.
If your A1C is 6.5 percent, your eAG is 140 mg/dL.
If your A1C is 7 percent, your eAG is 154 mg/dL.
If your A1C is 7.5 percent, your eAG is 169 mg/dL.
If your A1C is 8 percent, your eAG is 183 mg/dL.
If your A1C is 8.5 percent, your eAG is 197 mg/dL.
If your A1C is 9 percent, your eAG is 212 mg/dL.
If your A1C is 9.5 percent, your eAG is 226 mg/dL.
If your A1C is 10 percent, your eAG is 240 mg/dL.
Your eAG number may differ from what you typically see on your blood glucose meter or your meter average because it represents an average of your glucose levels 24 hours a day. The average on a meter is based on the number of checks you do. Because eAG is easier to understand, the ADA recommends that it become the preferred way to report A1C test results. Your doctor may already include the eAG on the form used to show you your test results.