Home >> ALL ISSUES >> 2014 Issues >> Diabetes debate: HbA1c or glucose?

Diabetes debate: HbA1c or glucose?

image_pdfCreate PDF

Anne Paxton

February 2014—If it were a boxing match, the debate over whether hemoglobin should be used to diagnose diabetes would place the odds-on favorite in the “Yes” corner. In the “No” corner would be the underdog. At least based on the mainstream consensus since 2010, HbA1c for diagnosis is well established as an alternative to measuring glucose.

At the July 2013 meeting of the American Association for Clinical Chemistry, where opposing sides on this question squared off in a debate, a quick vote beforehand showed “Yes” with a 20-to-one edge. But the speakers came armed with provocative data on comparative benefits and drawbacks, and both sides scored solid points.

Most of the debate centered on two questions: Which is more accurate, HbA1c or glucose? And with regard to diagnosing diabetes and predicting risk of complications, what are the most important things to measure anyway?

“Even though we’ve been measuring glucose in blood for 100 years, the question that comes up is: How accurate is a glucose result?” said moderator David Sacks, MB, ChB, FRCPath, senior investigator with the National Institutes of Health, in introductory remarks before the debate.

Dr. Sacks

Dr. Sacks

Not only is there the usual preanalytical and analytical variation, but there is also large biological variability among people and even within a single person, he pointed out. “That means for every one of you sitting here, if you are healthy, your fasting plasma glucose can have a coefficient of variation of up to 8.3 percent between today and tomorrow, even if everything’s the same.”

HbA1c is not a perfect alternative, but since 1993, when the NGSP (formerly the National Glycohemoglobin Standardization Program) launched efforts to standardize HbA1c, there has been a huge improvement in the assay, Dr. Sacks said. “The means are much closer to the target, and the standard deviations have been reduced considerably. So while HbA1c is not perfect, it’s getting progressively better over time.”

In Dr. Sacks’ view, there are substantial deficiencies in the glucose criteria for diagnosing diabetes. Hemoglobin A1c standardization has significantly improved the measure. “Of course there are deficiencies in hemoglobin A1c. But hemoglobin A1c can be measured accurately in the vast majority of subjects with hemoglobin variants.”

The FDA’s approval of Roche’s Tina-quant HbA1c Dx blood test last spring showed just how far the HbA1c assay has come, said Robert A. Vigersky, MD, director of the Diabetes Institute at Walter Reed National Military Medical Center. In contrast with coefficients of variation typical of HbA1c 20 years ago, “the coefficient of variation in this assay was 1.5 percent. And I think that actually makes a very good case for the use of HbA1c for diagnosis, because it has by far the least analytic variability or overall variability.”

The American Diabetes Association made a big shift in 1997 when it lowered the recommended cut point for diagnosing diabetes. “If you have a fasting plasma glucose of 126 mg/dL or greater, you have diabetes. And prior to 1997, it had been 140. And the reason for that change was that it became obvious from the data that complications, particularly the microvascular complications like retinopathy and nephropathy, were appearing in people who had blood sugars much lower than 140.”

CAP TODAY
X