Understanding the A1C

What is the A1C test?

The A1C test is a blood test that provides information about a person’s average levels of blood glucose, also called blood sugar, over the past 3 months. The A1C test is sometimes called the hemoglobin A1c, HbA1c, or glycohemoglobin test. The A1C test is the primary test used for diabetes management and diabetes research.

How does the A1C test work?

The A1C test is based on the attachment of glucose to hemoglobin, the protein in red blood cells that carries oxygen. In the body, red blood cells are constantly forming and dying, but typically they live for about 3 months. Thus, the A1C test reflects the average of a person’s blood glucose levels over the past 3 months. The A1C test result is reported as a percentage. The higher the percentage, the higher a person’s blood glucose levels have been. A normal A1C level is below 5.7 percent.

A1C Conversion chart

What A1C target should people have?

People will have different A1C targets depending on their diabetes history and their general health. People should discuss their A1C target with their health care provider. Studies have shown that people with diabetes can reduce the risk of diabetes complications by keeping A1C levels below 7 percent.

Maintaining good blood glucose control will benefit those with new-onset diabetes for many years to come. However, an A1C level that is safe for one person may not be safe for another. For example, keeping an A1C level below 7 percent may not be safe if it leads to problems with hypoglycemia, also called low blood glucose.

Less strict blood glucose control, or an A1C between 7 and 8 percent—or even higher in some circumstances—may be appropriate in people who have

  • limited life-expectancy
  • long-standing diabetes and difficulty attaining a lower goal
  • severe hypoglycemia
  • advanced diabetes complications such as chronic kidney disease, nerve problems, or cardiovascular disease

Points to Remember

  • The A1C test is a blood test that provides information about a person’s average levels of blood glucose, also called blood sugar, over the past 3 months.
  • The A1C test is based on the attachment of glucose to hemoglobin, the protein in red blood cells that carries oxygen. Thus, the A1C test reflects the average of a person’s blood glucose levels over the past 3 months.
  • In 2009, an international expert committee recommended the A1C test be used as one of the tests available to help diagnose type 2 diabetes and prediabetes.
  • Because the A1C test does not require fasting and blood can be drawn for the test at any time of day, experts are hoping its convenience will allow more people to get tested—thus, decreasing the number of people with undiagnosed diabetes.
  • In the past, the A1C test was not recommended for diagnosis of type 2 diabetes and prediabetes because the many different types of A1C tests could give varied results. The accuracy has been improved by the National Glycohemoglobin Standardization Program (NGSP), which developed standards for the A1C tests. Blood samples analyzed in a health care provider’s office, known as point-of-care (POC) tests, are not standardized for use in diagnosing diabetes.
  • The A1C test may be used at the first visit to the health care provider during pregnancy to see if women with risk factors had undiagnosed diabetes before becoming pregnant. After that, the oral glucose tolerance test (OGTT) is used to test for diabetes that develops during pregnancy—known as gestational diabetes.
  • The standard blood glucose tests used for diagnosing type 2 diabetes and prediabetes—the fasting plasma glucose (FPG) test and the OGTT—are still recommended. The random plasma glucose test may be used for diagnosing diabetes when symptoms of diabetes are present.
  • The A1C test can be unreliable for diagnosing or monitoring diabetes in people with certain conditions that are known to interfere with the results.
  • The American Diabetes Association recommends that people with diabetes who are meeting treatment goals and have stable blood glucose levels have the A1C test twice a year.
  • Estimated average glucose (eAG) is calculated from the A1C to help people with diabetes relate their A1C to daily glucose monitoring levels.
  • People will have different A1C targets depending on their diabetes history and their general health. People should discuss their A1C target with their health care provider.

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