Diabetes Experts Recommend A1c Testing for Diabetes Diagnosis

An international committee of diabetes experts has recommended that the hemoglobin A1c assay, which now is routinely used to monitor the course of disease in patients with diabetes and signal the pending development of diabetic complications, should become the new "gold standard" for diagnosing diabetes.

The committee, which was assembled by the American Diabetes Association, the International Diabetes Federation and the European Association for the Study of Diabetes, presented its recommendations June 5 during the ADA's 69th Scientific Sessions conference in New Orleans. The committee's report will be published in the July issue of Diabetes Care.

According to the committee, hemoglobin A1c values vary less than fasting plasma glucose, or FPG, levels, and A1c measurement has technical advantages compared with glucose testing. In addition, whereas both the FPG test and the less commonly used oral glucose tolerance test, or OGTT, require patients to fast, the A1c test does not.

"It's going to be easier for family physicians to make a diagnosis," said Michael Parchman, M.D., the AAFP representative to the National Diabetes Education Program convened by NIH's National Institute of Diabetes and Digestive and Kidney Diseases and the CDC.

Parchman, who is the Mario E. Ramirez Endowed Distinguished Professor in the department of family and community medicine at the University of Texas Health Science Center at San Antonio, said physicians often must schedule a second appointment for patients they suspect may have diabetes if the FPG test or OGTT is used as the diagnostic tool.

"Sometimes, that could be a problem because of (patients' issues with) transportation, mobility or scheduling," he said. "Now, if you suspect diabetes, you can draw blood and send it to the lab right then. You don't have to have them come in at a future date, which they might not be able to do. You don't have as much problem with follow-up, and fewer patients fall through the cracks."

A1c testing measures a person's long-term (i.e., preceding two to three months) blood glucose exposure. That aspect of the test, said Parchman, gives physicians a more comprehensive understanding of a patient's overall health than other commonly used tests. According to the committee report, it also makes the A1c test a better predictor of a patient's risk for complications than single or episodic measures of glucose levels.

"It shows the degree of glucose exposure over time better than a one-point-in-time glucose tolerance test," he said. "It's not the kind of thing where a person can change (his or her) diet and level of exercise for a short period of time and have a good test. You can't fudge it."

Committee members concluded that using an A1c cut-point of 6.5 percent or higher to establish the diagnosis of diabetes was justifiable, although they recommended that the diagnosis be confirmed with a repeat A1c test unless the patient displays clinical symptoms and has glucose levels greater than 200 mg/dl.

People with an A1c level of at least 6 percent but less than 6.5 percent likely are at high risk for developing diabetes, said the committee report.

The committee also said A1c values are more stable after collection compared with the other tests. According to the report, glucose levels in whole blood samples taken from nondiabetic patients have been known to decrease by 3-10 mg/dl in as little as one to four hours when kept at room temperature -- even when collected in sodium fluoride.

"That's not an issue with A1c," Parchman said. "It's less sensitive to how it's handled or how long it takes you to run the test. But it is important to note that the test should be run on a calibrated instrument like those present in most diagnostic laboratories. The current in-office, point-of-care A1c tests are much less reliable for making a diagnosis and should not be used for that purpose."

Despite its advantages, A1c testing has not become widely accepted as a diagnostic tool because of its lack of assay standardization. Although expert panels considered this option in 1997 and again in 2003, they recommended against it, in large part, for that reason.

However, the new report noted, "An updated examination of the laboratory measurements of glucose and A1c by the current International Expert Committee indicates that with advances in instrumentation and standardization, the accuracy and precision of A1c assays at least match those of glucose assays."