Diabetes and the A1C Test: What Does It Tell You?

Blood sample on microscopic slide
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The A1C test (also known as HbA1C, hemoglobin A1c, glycated hemoglobin or glycosylated hemoglobin) is a good general measure of diabetes care. While conventional home glucose monitoring measures a person’s blood sugar at a given moment, A1C levels indicate a person’s average blood glucose level over the past two-to-three months.

How Does it Work? 

You can retrieve an A1C test through regular blood draw.

Many doctors offices also have A1C testing machines and are able to retrieve the result with a small drop of blood that is obtained from pricking the finger with a lancet. You do not have to be fasting to receive an A1C test which makes it more convenient and more likely to be done.

Hemoglobin A, a protein found inside red blood cells, carries oxygen throughout the body. When there is glucose in the bloodstream, it can actually stick (glycate) to the hemoglobin A protein. More glucose in the blood means that more glucose sticks to hemoglobin and a higher percent of hemoglobin proteins become glycated.

Once glucose sticks to a hemoglobin protein, it typically remains for the lifespan of the hemoglobin A protein—as long as 120 days. Therefore, at any moment, the glucose attached to the hemoglobin A protein reflects the level of the blood sugar over the last two to three months.

The A1C test measures how much glucose is actually stuck to hemoglobin A, or more specifically, what percent of hemoglobin proteins are glycated.

Thus, having a 7 percent A1C means that 7 percent of the hemoglobin proteins are glycated.

Understanding A1C Numbers

For a person without diabetes, a typical A1C level is about 5 percent. A borderline A1C is considered 5.7-6.4 percent (this is considered prediabetes). For someone with diabetes, experts disagree somewhat on what the A1C target should be.

The American Diabetes Association (ADA) recommends an A1C target of less than or equal to 7 percent. The American Association of Clinical Endocrinologists recommends a level of 6.5 percent or below.

The ADA also emphasizes that A1C goals should be individualized. Those with diabetes should check with a healthcare professional to learn what their A1C targets should be. For example, for those people who have reduced life expectancy, long standing diabetes and difficulty attaining a lower goal, severe hypoglycemia, or advanced diabetes complications such as chronic kidney disease, nerve problems, or cardiovascular disease the A1C target goal might be higher. 

However, for most people, a lower A1C is ideal so long as they are not having frequent bouts of low blood sugars. In fact, the National Institutes of Health (NIH) says that, in general, every percentage point drop in an A1C blood test results (e.g., from 8 percent to 7 percent) reduces the risk of eye, kidney and nerve disease by 40 percent.

A1C to eAG Estimated Average Glucose Levels

Note that the A1C is not the same as the estimated average glucose (eAG), which is the two to three-month average in mg/dL, but the A1C directly correlates to the eAG.

When you are testing your blood sugars daily, the numbers you see on your monitor are also measured in mg/dL. They reflect a moment in time and are not the same as your eAG.

The A1c percentage can be translated into an estimated average blood sugar. For example, an average blood glucose of 150 mg/dL (milligrams per deciliter) translates into an A1C of about 7 percent. This is above normal, given that a diagnosis of diabetes is usually given when blood sugar levels reach about 126 mg/dL.

A1c to eAG Conversion Chart

HbA1c or A1ceAG
%mg/dlmmol/l
61267.0
6.51407.8
71548.6
7.51699.4
818310.1
8.519710.9
921211.8
9.522612.6
1024013.4

The formula used is: 28.7 X A1C - 46.7 = eAG.

How Often is the A1C Test Is Necessary? 

The American Diabetes Association recommends that all people over 45 (who are not symptomatic) get screened for diabetes. This may mean that they receive an A1C test once every three years. If on the other hand, someone has a strong family history of diabetes or other high risk factors it may be recommended to get checked sooner. Additionally, if someone is symptomatic and are experiencing—increased thirst, increased hunger, increased urination or fatigue, an A1C test can be used as a diagnostic tool. 

People with diabetes should have their A1C tested every three months; if blood sugars are fairly stable at near-normal levels, twice a year may be enough. Health care providers should tell patients what is right for them and enable them to monitor their diabetes management more easily. More frequent A1C tests may be recommended if someone has recently changed his or her treatment plan.

The A1C Test is Used in Diagnosing Diabetes and Prediabetes 

The A1C test can be used in diagnosing diabetes and prediabetes. In some instances, an A1C test can be used as a second test to verify if a person is at risk or has diabetes or prediabetes. For example, if you have an elevated fasting blood sugar or greater than 126 mg/dL and your health care provider is suscpicious of diabetes, he can order an A1C test to confirm. According to the National Institute of Health, when the A1C test is used soley for diagnosis, the blood sample must be sent to a laboratory that uses an NGSP-certified method for analysis to ensure the results are standardized.

How Accurate is the A1C Test?

The National Institute of Health states, "The A1C test result can be up to 0.5 percent higher or lower than the actual percentage. This means an A1C measured as 7.0 percent could indicate a true A1C anywhere in the range from ~6.5 to 7.5 percent. Health care providers can visit www.ngsp.org  to find information about the accuracy of the A1C test used by their laboratory."

But, it's important to keep in mind that all types of blood tests are subject to some variability. 

The Limitations of the Test

While the A1C is a good measure of overall glucose control, it cannot replace self-testing of blood glucose. Like other tests, results may vary from lab to lab. The A1C test is not calibrated the same everywhere, though an international effort is underway to standardize the A1C test to a new International Federation of Clinical Chemistry and Laboratory Medicine standard.

And there are some instances when an A1C test is not a good test to use. For example, some health conditions can result in falsely high A1C results or falsely low A1C results. 

False A1C results occur in people with other problems that affect their blood or hemoglobin. For example, a falsely low A1C result can occur in people with anemia, such as sickle cell anemia or thalassemia or those with heavy bleeding. On the other hand, a falsely elevated A1C result can occur in people who are very low in iron, for example, those with iron deficiency anemia.

Other causes of false A1C results include

  • kidney failure
  • liver disease

If you are wondering whether or not the A1C test is right for you, you can retrieve more information from the National Glycohemoglobin Standardization Program. They provide information for health care providers about which A1C tests are appropriate to use for specific hemoglobin variants at www.ngsp.org

A Word From VeryWell

The A1C test is a good general measure that is used to determine the average blood sugar of a person over the course of two-to-three months. The A1C test is used as a surveillance tool for those who have diabetes, as well as a screening and diagnostic tool tool for determining diabetes risk and diagnosis. You do not have fast to receive an A1C test and depending on your physician's facility you may be able to get your A1C done with real time results in his office. Additionally, other variables, such as your overall health, age, and blood sugar levels, will help to dictate individual acceptable A1C range as well as how often you should be tested. Sometimes an A1C test will not be an appropriate measure of blood sugar, especially if you are someone with a history of sickle cell anemia or advanced kidney disease. If you have any questions about your A1C, ask your health care team.  

Sources:

View Article Sources
  • National Institute of Diabetes and Digestive and Kidney Diseases. The A1c test and diabetes. 
  • American Diabetes Association. A1C Test.
  • American Association for Clinical Chemistry.. A1C: The Test..
  • National Glycohemoglobin Standardization Program.  IFCC Standardization of HbA1c. http://www.ngsp.org/