Using Hemoglobin A1c to Diagnose Diabetes: What’s Your Take?

Photo courtesy of Flickr Creative Commons user Scribbletaylor

The American Diabetes Association’s decision earlier this month to officially endorse hemoglobin A1c as a diagnostic test for diabetes is either timely, inappropriate, or long overdue, depending on whom you talk to.

In its 2010 Standards of Medical Care in Diabetes, the ADA for the first time officially endorsed the use of HbA1c as one of four options for diagnosing diabetes, with a cut-point of 6.5% or greater. Recommendations for use of the three previous diagnostic criteria remain unchanged, including a fasting plasma glucose of 126 mg/dL or above, a 2-hour plasma glucose of 200 mg/dL or greater on the oral glucose tolerance test, or a random glucose of 200 mg/dL or greater in someone with classic symptoms of hyperglycemia.
Although some experts have been urging use of the HbA1c to diagnose diabetes for many years—citing its greater convenience, among other advantages—the lack of global standardization precluded a recommendation for doing so until recently, according to Dr. Silvio Inzucchi of Yale University, New Haven, Ct., who chaired the ADA ad hoc working group that wrote the guideline.

Use of HbA1c for diabetes diagnosis was initially endorsed as a consensus opinion last summer by an international expert committee. The ADA working group reviewed that paper and arrived at similar conclusions (except that ADA did not say HbA1c is the “preferred” test).

“There is an inherent attractiveness to using the A1c, since it measures glucose exposure over a long period of time, not just the specific instance of when the blood test is obtained. … In all, the recent guidelines gives practicing clinicians another tool to screen patients who are at risk for diabetes,” Dr. Inzucchi said.

But Dr. Zachary T. Bloomgarden of Mount Sinai School of Medicine, New York, said ADA’s move is “overall, not to my mind satisfactory.”  Although he says he believes HbA1c could be used to screen people who would then undergo further testing, he says its use as a stand-alone diagnostic test could lead to overdiagnosis of “high glycators” or underdiagnosis of “low glycators,” each of whom comprise about 10% of the population.

At the other extreme is Dr. Mayer Davidson of the University of California, Los Angeles, who has been advocating use of the HbA1c to diagnose diabetes for more than a decade.  In fact, he says he believes it should be the only test: “Unfortunately, the ADA kept the glucose criteria, which will lead to the confusing situation of people who have diabetes by one criterion but not by the other when both are measured, which is likely to occur frequently.”

So will the new endorsement change clinical practice? In a 2005 survey of 258 internists, 93.4% reported that they routinely screened for diabetes, 49% reported using HbA1c for screening, and 58% said they used it for diagnosis of diabetes. Interestingly, 49% mistakenly thought HbA1c was already an approved screening test (J. Clin. Endocrinol. Metab. 2008;93:2447-53).

–Miriam E. Tucker (@MiriamETucker on Twitter)

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4 Comments

Filed under Endocrinology, Diabetes, and Metabolism, Family Medicine, Geriatric Medicine, IMNG, Internal Medicine, Polls, Primary care

4 responses to “Using Hemoglobin A1c to Diagnose Diabetes: What’s Your Take?

  1. Awareness is an important key when pushing the testing initiative and that should be where we concentrate most resources.
    Yes the a1c test is another tool in the arsenal, but what good is it if we have an epidemic-level disease that few people know the facts about.

  2. A1C testing used as another tool to diagnose people is awesome! fasting blood sugar can be low. Doctor gets the results back. “OH, Sue doesn’t have diabetes. Great fasting number.” um, I totally disagree with the current method. A1C goes back 3 months and provides more of a story than a one page book. Sorry, of I confused you.

  3. Pingback: The Top-Viewed Posts of 2010 | EGMN: Notes from the Road

  4. Mariaelena Calhoun

    At our Pediatric Diabetes Center, we treat 1600-1700 children with Diabetes. About 10% are type 2. Many of these children have insulin resistance and glucose intolerance for a period of time (sometimes years). If we used a stand alone A1C as the diagnostic criteria, we would flood our education team with patients.

    Some of these children who have an A1c 6.5%. Often they have a negative 2 hour OGTT. This is a population that consumes a great deal of calories of refined sugars, soda/juice, and junk food. With lifestyle intervention many of the A1cs decrease. Hopefully with maintained lifestyle intervention and weight loss, they are able to maintain A1cs of <6.5. They are treated in our Metabolic Clinic until they have a confirmation of diabetes. A1c of 6.5 % or greater should prompt further lab investigation and prompt action to change lifestyle. In these stressed economic times, we cannot afford the personnel to provide expensive diabetes education.

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