A1C Tests: Questions and Answers

by David Mendosa Patient Advocate

To make sure that your blood glucose level isn’t too high, you need to get regular checks of your long-term level. The A1C test measures your blood glucose during the past few months, and “has strong predictive value for diabetes complications.”

Carbohydrate rich foods.

What does the A1C measure?

The A1C tests you take tell you and your doctor if too much sugar stays in your blood and doesn't get to the cells that need energy. The test measures the percentage of hemoglobin, the blood’s oxygen-carrying molecule, that is tied up to glucose. That’s why its technical name is Hemoglobin A1c, which is usually abbreviated to HbA1C or A1C.


Why do people say it only measures the "past few months"?

How much of your hemoglobin is bound to glucose depends both on the amount of glucose that stuck in your blood and also on the lifespan of your own red blood cells. While this varies from person to person, the average lifespan is 120 days. Half of your A1C level depends on the previous month, one-fourth comes from days 30 to 60, and the other fourth come from days 60 to 120.

Doctor checks patient's blood sugar.

Can A1C tests diagnose diabetes?

Yes. In 2009 an International Expert Committee determined that the A1C test is one of three ways diabetes can be diagnosed. Based on prevalence of retinopathy, a serious complication of uncontrolled diabetes, A1C levels of 6.5 percent or more means you have diabetes. Both the ADA and the WHO endorsed this recommendation. A1C levels between 5.7 and 6.4 percent now indicate "prediabetes," with a high risk of developing diabetes.


What do the numbers mean?

If your A1C number is higher than 6.0 percent, it’s higher than normal, and you have a greater risk of diabetes complications. The normal range is 4.0 to 6.0 percent, according to the major laboratories and the standard chemistry textbook. The lower your A1C level the lower your risk. But people with hemolytic diseases like the sickle-cell trait or recent significant blood loss can have falsely lower values.


What should I do if my number is high?

You need to bring your A1C level down to a range recommended by your physician. Treatment goals may vary and depend on each patient’s individual situation. Because A1C is an indicator of your blood sugar over the last few months, the change in A1C won’t be seen immediately. But you can use the information about your level to talk to your doctor about diet or medication changes you should make.


How often can I get my A1C checked?

As often as you like! Since half of the A1C level comes during the previous month, it makes sense to check your A1C more often than the ADA’s recommendation of at least twice a year, I wrote in 2012. And note that the ADA does recommend that the A1C be done quarterly if there has been a change in therapy or if A1C goals have not been met. I now check my level every month or two. Now that an accurate and inexpensive home A1C test is available, you don’t have to make a trip to your doctor’s office or lab for it.


What's the relationship between A1C and eAG?

The eAG is short for estimated average glucose, and it’s expressed in the same units that we use to measure finger stick results, mg/dl. But it’s not the same as the average of your finger stick numbers. Instead, it’s just a way to convert the percent amount that we usually use to measure A1C. A few years ago the ADA made a big push to use the eAG, but it hasn’t caught on and isn’t yet generally accepted.


What doesn't the A1C measure?

The A1C is the gold standard in diabetes testing. But one test can’t measure everything. It doesn’t provide a measure of glycemic variability or hypoglycemia. Glycemic variability is how much your blood glucose fluctuates between high and low levels. If you have significant fluctuations — and especially if you have type 1 diabetes or type 2 diabetes with severe insulin deficiency — you can use a continuous blood glucose monitor to get a better view of the variability.


What should my A1C goal be?

For most people “a reasonable A1C goal” is less than 7 percent, the ADA says. It adds that some of us can set it higher or lower, depending on different factors in our situations and histories. For example, less stringent goals may be appropriate for someone with a history of severe hypoglycemia or a limited lifespan. More stringent goals are appropriate for someone who is not experiencing hypoglycemia or other adverse effects of treatment.

David Mendosa
Meet Our Writer
David Mendosa

David Mendosa was a journalist who learned in 1994 that he had type 2 diabetes, which he wrote about exclusively. He died in May 2017 after a short illness unrelated to diabetes. He wrote thousands of diabetes articles, two books about it, created one of the first diabetes websites, and published a monthly newsletter, “Diabetes Update.” His very low-carbohydrate diet, A1C level of 5.3, and BMI of 19.8 kept his diabetes in remission without any drugs until his death.