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A1C Levels may one day be used for diagnosis

Aug 19, 2008

Fasting Glucose over 126mg/dl or 2 random glucose readings over 200mg/dl mean your patient has diabetes. But what about their A1c? We use to measure therapy success, but what about using A1c to diagnose diabetes? According to David Sacks, MD, Assistant Professor of Pathology Harvard Medical School we should be officially doing that now. Click here to learn how that might change

A1C Levels may one day be used for diagnosis
David Sacks, MD, Assistant Professor of Pathology at Harvard Medical School

Diabetes may be diagnosed using HbA1C in the near future, according to a presentation last week, from David Sacks, MD, Assistant Professor of Pathology at Harvard Medical School.  In fact, Dr. Sacks said that anecdotal evidence suggests many physicians are already using A1C to diagnose diabetes, even though there has been no cut-off level established for diagnosis.

“What are the advantages of using A1C in diagnosis?
It indicates chronic hyperglycemia — you can’t cheat,” Dr. Sacks said. Because A1C measures the concentration of glycated hemoglobin and red blood cells live for months, the test cannot be easily skewed, as plasma glucose tests can be.
In addition to the fact that fasting plasma glucose can be skewed easily by patients’ behavior,  the numbers are not extremely reliable in the first place, according to Dr. Sacks. He explained confidence intervals in laboratory tests. For instance, lab results indicating a plasma glucose of 126 mg/dL could really mean that — after applying the coefficient of variability for an individual, plus the confidence interval of a laboratory test — this patient would test between 101 and 151 mg/dL 95 percent of the time.

“It’s just the reality. I try to explain to people that you have to understand the limitations of lab tests to use them properly,” Dr. Sacks said.  He explained that the standardization of A1C testing by the National Glycohemoglobin Standardization Program (NGSP) in 1990s has made the measurement reliable. Now 99 percent of patients with an A1C above 7 percent have diabetes.

“I think in the future we can expect to see A1C used for diagnosis,” Dr. Sacks said. The American Diabetes Association and the European Association for the
Study of Diabetes have created a task force to review diagnosing and screening for the disease. “This will be the first time that the ADA and EASD have come out together with recommendations.”

Dr. Sacks also discussed an exciting development in average glucose measurements. The HbA1C-derived Average Glucose study released results in 2007 showing a standardized formula for AG using A1C. The study tracked 507 people, 427 of whom had diabetes, during three months. They used self-measurement of blood glucose as well as continuous glucose monitoring to gather 2,700 measurements for the group. The ADA has initiated an education campaign to have the new AG formula included in laboratories that measure A1C, so health care providers are now able to get both measures back with A1C results.

The new formula derives AG measurements lower than those derived from the previous formula resulting from DCCT.

Dr. Sacks also cleared up any confusion lingering about the NGSP standardized A1C measurements versus the standard International Federation of Clinical
Chemistry A1C measures. Those from the IFCC, he pointed out, are not appropriate for patient testing and the standard will remain the NGSP measurement.


David Sacks, MD, Assistant Professor of Pathology at Harvard Medical School.