Medically Reviewed By: Tom Iarocci, MD

The A1C blood test is an indicator of the average blood glucose, or blood sugar levels, for any given person over the previous two to three months. The test is also known as the glucohemoglobin, HbA1c, or hemoglobin A1c test. It is one of the most useful tests in the management of diabetes and it’s also frequently used in medical research and in clinical studies on diabetes.

How Does It Work?

The test looks at hemoglobin to determine how “sugared up” it has become. Hemoglobin is the red blood cell protein that carries oxygen. These red cells constantly die and new ones form, but they have an average lifespan of about four months. Some red cells have had more time to get sugared up, or glycated, and others are brand new and have had less time to show their exposure to sugar, so there is an averaging effect. Hence, by completing an A1C test, doctors can see what the average blood glucose levels were over the past two-to-three months. The result of this test is expressed in a percentage, which can be though of as “percent sugared up.” In general, the higher the percentage, the higher the average blood glucose levels have been.

The A1C Test for Diagnostic Purposes:

Normally, in people without diabetes, an A1C level should be 5.7% or less.

When results go above 5.7% this is suggestive of the possibility a diagnosis of prediabetes or diabetes. The A1C test can be used both to diagnose type 2 diabetes and to identify prediabetes. One of the strengths of the A1C test is that you do not have to fast before you have it performed. This also means that blood can be drawn from the patient at any time of the day, rather than specifically in the morning.

How Can the Results Be Used for Diagnostic Purposes?

The A1C test can be used as a standalone test, or in combination with other tests, in order to diagnose diabetes and prediabetes. When used for diagnostic purposes, the blood sample has to be investigated by a laboratory where “NGSP certified” testing and analysis methods are present. This ensures that standardized results are obtained. Still, there can be variation in a single A1C result from even a standardized laboratory. If an A1C is elevated and a person has symptoms of diabetes, however, the two findings together drastically reduce any diagnostic uncertainty. In other words the chances of a false positive A1C in that case would be low.

What Is Average Blood Sugar A1C Level?

The first thing to know when looking for what is average blood sugar A1C level is that anything below 5.7% is normal. That is also the average. However, for those who score between 5.7% and 6.4%, this can be indicative of prediabetes. Likewise a result of 6.5% or above is indicative of full-fledged diabetes.

If you are diagnosed with prediabetes, it means you are at risk for developing type 2 diabetes in the future. People with prediabetes are usually re-tested often and encouraged to do some of the things that have been shown to keep blood sugar levels from rising toward the levels seen in full-fledged type 2 diabetes. This includes eating healthy foods that are low in fat and calories and high in fiber, being physically active, losing excess weight, quitting smoking, and, if needed, starting medications to help with the glucose control.