A1c: Points to Remember

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• 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 pre-diabetes.
• 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 pre-diabetes 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 ADA 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.