Should the Hemoglobin A1C Test Be Used to Diagnose Diabetes?

The pros and cons of using the hemoglobin A1C test to diagnose prediabetes and diabetes was the subject of a lively debate at the American Association of Clinical Endocrinologists 19th Annual Meeting. Richard M. Bergenstal, MD, Executive Director of the International Diabetes Center at Park Nicollet, Minneapolis, Minnesota, argued in favor of the A1C test. Taking the opposing position was Zachary T. Bloomgarden, MD, professor of clinical medicine at Mt. Sinai College of Medicine in New York.

“In a standardized laboratory it is a better test in so many ways,” said Bergenstal. “It is better than fasting plasma glucose or the two hour oral glucose tolerance test. It is a good index for overall glycemic exposure. There’s less biologic variability. All of us know the issues that can arise when our fasting blood glucose samples do not go immediately to the lab to be analyzed. Why wouldn’t you use A1C?”

Bergenstal also said that he was not convinced that the oral glucose tolerance test I has to be the gold standard against which all other tests are weighed. “High A1Cs predict retinopathies. The A1C seems to be the most accurate within a given individual and within a population, and it seems to be the best predictor of future development of diabetes or of morbidity and mortality and heart disease.”

The A1C is also very useful to identify individuals with prediabetes, or at risk for prediabets. “The results from the test will allow us to intervene and implement some cost-effective strategies to prevent people from getting diabetes,” he said.

Bloomgarden countered that the factors influencing hemoglobin A1C are very complex. “There is a long shopping list of things that can affect the results of the test, including vitamin deficiency and iron deficiency. There are so many different things to take into account and often, physicians are not cognizant of them,” he noted.

He also pointed out that the notion that A1C links directly with actual blood sugar levels is false. “That idea that there is an estimated average glucose and if your A1C is 6.5 your average glucose is going to be right on the dot at 152 may or not be correct.

Hemoglobin A1C results may differ among ethnic populations. For example, studies have shown that African Americans can have higher A1C levels than Caucasians, despite having lower blood sugars.

Bloomgarden also said that the accuracy of A1C testing touted by Bergenstal is not actually achieved in clinical laboratories in the US. “Also consider that many clinicians use point of care A1C testing in their offices, which is considerably less accurate, but is still being used to make the diagnosis of diabetes. As a result, we can wind up with a dilemma.”

He concluded: “My basic feeling as a clinician is that diabetes is glucose. If we lose sight of the reality of glycemia, then we may be misled in diagnosing our patients, and perhaps in treating our patients.”