Experts Recommend that Hemoglobin A1c also be used to Diagnose Diabetes

The committee said it intends its report to serve as a stimulus to the international community and professional organizations to consider the use of the A1C assay to diagnose diabetes. The American Diabetes Association said it endorses the report "in principle" and will establish a task force to explore the implications of implementing the recommendations.

Doctors have relied on fasting plasma glucose (FPG) and oral glucose tolerance tests (OGTT) to diagnose diabetes for many years (see Glucose). The committee suggests that A1c should replace both FPG and OGTT as the test of choice to diagnose diabetes, because several studies have shown that A1c "is related more intimately to the risk of complications than single or episodic measures of glucose levels, may serve as a better biochemical marker of diabetes, and should be considered a diagnostic tool." In recent years, the accuracy and precision of A1c tests have improved so that they are at least as precise and accurate as FPG tests, the recommendation adds. (For more about the A1c test, click here.)

A Long Road to Change
In 1979, the National Diabetes Data Group first recommended FPG tests to diagnose diabetes, considering a glucose level of 140 mg/dL (7.7 mmol/L) or higher to be abnormal. In 1997, the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus evaluated studies looking at the relationship between laboratory test results and long-term complications of diabetes and lowered the cutoff for FPG to greater than or equal to 126 mg/dL (7.0 mmol/L). The studies also showed a relationship between A1c results and diabetic complications, but the 1997 guidelines did not recommend A1c levels for diagnosing diabetes, mainly because of lack of standardized tests for A1c.

Since 1997, advances in standardization and instrumentation have led to A1c precision and accuracy that at least match those of glucose tests, the recommendation notes. These improvements, coupled with several advantages of A1c, drive the suggested switch to A1c as a diagnostic test. In addition, A1c requires no special preparation (such as fasting overnight), making testing for diabetes much easier.

How High is Too High?
A1c levels of 6.5% or more are associated with an increased risk of blood vessel damage (detected in the eye as retinopathy), so the committee recommends that they prompt a diabetes diagnosis and confirmation with a repeat A1c test. If your A1c level is over 6.0%, you and your doctor should take measures to prevent the disease, the statement adds. If your A1c level is lower than 6.0%, preventive measures may be warranted if you have a family history of the disease, a high body mass index, or elevated blood pressure and triglyceride levels.

The statement discourages doctors from "mixing and matching" A1c, FPG, and OGTT results because the tests don't correlate completely and doing so can lead to confusion.

The statement also discourages use of the terms "pre-diabetes" and "impaired glucose tolerance" and suggests that they be discontinued because they fail to "capture the continuum of risk." "Pre-diabetes" especially implies that people diagnosed as such will get the disease, which isn't necessarily the case, David M. Nathan, MD, of Harvard Medical School said recently at a meeting of the American Diabetes Association.

The committee specifically recommends that for diagnostic purposes, A1c tests should be performed in clinical laboratories and not using point-of-care tests (POCT), which are not as accurate or precise. While the committee's statement makes clear its preference for A1c as a diagnostic test, it recognizes that the test may not be appropriate in all situations. This may be true for developing countries because it is more expensive than the other tests and because certain countries have high rates of chronic anemia, which can interfere with A1c tests. A1c is not recommended for use in diagnosing diabetes in pregnancy or in children with type I diabetes because glucose levels usually increase before A1c in those conditions. Results of some A1c tests may be affected if a patient has a hemoglobinopathy. Those who have this condition should talk to their doctor if having an A1c test done.

A number of other studies have also recommended that criteria for diagnosis of diabetes be changed to include A1c but have not gone as far as the current study to suggest that it become the preferred test. At present, the American Diabetes Association is considering this recommendation.

Martha Kerr. ADA 2009: Expert Committee Recommends Use of Hemoglobin A1C for Diagnosis of Diabetes. Medscape.com. Available online at http://www.medscape.com/viewarticle/704021?src=rss through http://www.medscape.com. Accessed July 2009.

Press release. International Expert Committee Recommends New Way To Diagnose Diabetes. American Diabetes Association. Issued June 5, 2009. Available online at http://www.diabetes.org/for-media/pr-international-expert-committee-recommends-new-way-to-diagnose-diabetes.jsp through http://www.diabetes.org. Accessed July 27, 2009.