"Glucose impairment runs on a continuum, making selection of a specific value where diabetes risk begins somewhat arbitrary," Nathan said. "However, those persons whose A1c levels are close to the 6.5 percent diagnostic level are clearly at higher risk."
The committee also recommended screening all adult patients who are overweight and have other risk factors, such as family history of diabetes, high blood pressure or an abnormal blood lipid profile.
"What the test will do is to give the clinician and the patient a better integrated view of the average blood sugar," said Montefiore's Zonszein.
Dr. Christopher D. Saudek, a Johns Hopkins Hospital endocrinologist, agreed, adding that the main advantage of the A1c is that it "does not require fasting, so it can be done any time of day."
Also, he noted, because it measures glucose levels over months, rather than at the moment of a blood test, "it is less susceptible to patients 'tuning up' before they see a doctor [by] watching their diet for a day or two."
Until now, some practitioners say, diabetes specialists have favored the more finely-tuned FPG and glucose tolerance measurements, while primary care doctors have been more willing to embrace the A1c.
To Dr. Thomas L. Schwenk, a professor of family medicine at the University of Michigan in Ann Arbor, this reflects different approaches to different patient populations. He said the A1c makes more sense in his practice.
"We are dealing with patients with many chronic problems and the obvious need for major lifestyle modifications, as well as managing six to eight medications directed at metabolic syndrome, not making decisions about tweaking insulin dosages by a couple units," he said.
Most agree that the A1c will reflect a more realistic pool of patients with diabetes and pre-diabetes.
It will help "chip away at the 40 percent of people with diabetes who don't know it," Saudek said.