A1C Tests: Questions and Answers

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To make sure that your blood glucose level isn’t running 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.” (All images credit: Thinkstock)

What does the A1C measure?

The A1C tests you take tell you and your doctor if too many of the carbohydrates you eat stay in your blood and don’t get to the cells that need energy. They measure the percentage of your blood that carries oxygen, hemoglobin, which 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.

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% or more means you got it. Both the ADA and the WHO endorsed this recommendation. A1C levels between 5.7 and 6.4% now diagnose prediabetes with a high risk of developing diabetes.

What do the numbers mean?

If your A1C number is higher than 6.0%, it’s higher than normal, and you have a greater risk of diabetes complications. The normal range is 4.0 to 6.0%, 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 at least to 6.0% as quickly as possible. Because it measures your level over the past few months, it’s impossible to do that immediately. But you can use the information about your level to cut back on the amount of carbohydrates you eat. You can also ask your doctor if you should change your diabetes medicine or take more of it.

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. I now check my level every month or two. And 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 test. 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’ve got this -- especially if you have type 1 diabetes or type 2 diabetes with severe insulin deficiency -- you can use a continuous blood glucose monitor.

What should my A1C goal be?

For most people “a reasonable A1C goal” is less than 7%, ADA says. It adds that some of us can set it higher or lower. But you want to minimize the risk of complications, the lower the level you reach the better. At first it must at least be in the normal range, which is less than 6.0%. Later you can set it as complete remission from diabetes, which is an A1C level of less than 5.6 for a year or more.