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Diagnostic threshold set at 100 mg/dL
Lower Fasting Glucose Cutoff, More Prediabetes

Miriam E. Tucker
Senior Writer

New guidelines from the American Diabetes Association will place even more people into the “prediabetes” category.

The ADA's Follow-up Report on the Diagnosis of Diabetes Mellitus reduces the lower limit for the diagnosis of “impaired fasting glucose (IFG)” from 110 to 100 mg/dL, and redefines “normal” as a fasting plasma glucose (FPG) of less than 100 mg/dL (Diabetes Care 26[11]:3160-67, 2003).

Other diagnostic thresholds related to impaired glucose regulation that the ADA defined in 1997 remain the same: Diabetes is diagnosed at a fasting plasma glucose of 126 mg/dL or above, and the cutoffs for the 2-hour oral glucose tolerance test remain at 140-199 mg/dL for impaired glucose tolerance (IGT) and 200 mg/dL or greater for diabetes. As before, the diagnosis of diabetes requires a confirmatory test on a separate day (Diabetes Care 20[7]:1183-97, 1997).

Data acquired since 1997 suggest that the new cutoff of 100 mg/dL better correlates with a 2-hour plasma glucose value of 140 mg/dL and more accurately identifies the population at greatest risk for progression to type 2 diabetes in the absence of intervention. “This new FPG cutoff gave us the best combination of sensitivity and specificity,” ADA expert committee chair Dr. Saul Genuth told this newspaper.

In a recent review of data from around the world, only half or less of people with IFG by the old cutoff also had IGT and an even lower proportion (20%-30%) of those with IGT also had IFG (Diabet. Med. 19[9]:708-23, 2002). The new cutoff is expected to increase the proportion of people with IFG who would also have IGT.

Some studies aimed at teasing out identifiable differences between the two groups have yielded conflicting data.

“At this point in time, there is no clear pathophysiologic basis for explaining IFG versus IGT. All we know is that both are at risk to go on to diabetes,” commented Dr. Genuth, who is professor of medicine at Case Western Reserve University, Cleveland.

The ADA report notes that although the 2-hour oral glucose tolerance test probably will remain a more sensitive assay for detecting diabetes, the FPG is more reproducible, less costly, and likely to be more convenient in routine clinical practice. (As in 1997, the hemoglobin A_1c test is still not recommended for the diagnosis of diabetes.)

The new IFG definition takes on particular significance in an era of dramatically rising rates of obesity, diabetes, and cardiovascular risk. It also follows on the heels of major study findings suggesting that diet, exercise, and certain medications can stem the progression to diabetes among people at risk.

Last year, the ADA and the U.S. Department of Health and Human Services issued a document on the prevention or delay of type 2 diabetes in individuals with IFG or IGT, urging physicians to screen individuals at high risk and to implement nutrition and physical activity interventions in those identified as having “prediabetes” (Diabetes Care 25[4]:742-49, 2002).

At that time, the ADA estimated that at least 16 million Americans aged 40-74 had prediabetes. Although it is not clear exactly how many more individuals will now fall into the prediabetic category with the new FPG cutoff, the total probably will exceed 20 million and perhaps even reach 30 million, according to ADA expert committee member Dr. John Buse, director of the Diabetes Care Center at the University of North Carolina at Chapel Hill.

Unlike the diabetes fasting blood glucose cutoff of 126 mg/dL, which was derived based on its correlation with development of retinopathy, the 100-mg/dL FPG cutoff does not specifically identify a threshold for cardiovascular disease, which is the cause of death in more than 70% of people with type 2 diabetes.

“It will be very important to know whether the prevention of progression from IFG to diabetes will also prevent the development of cardiovascular disease,” Dr. Genuth noted.

The answer to that could come from a long-term follow-up of participants in the landmark Diabetes Prevention Program, the major U.S. trial that achieved a 58% reduction in progression to type 2 diabetes among individuals with IGT who followed a strict diet and exercise regimen, and a 31% reduction among those who took metformin for 3 years (N. Engl. J. Med. 346[6]:393-403, 2002).

In the meantime, the new IFG definition should help focus attention yet again on the importance of lifestyle intervention both for preventing diabetes and for improving overall health, both physicians told this newspaper.

“If lowering this number a little puts more people into serious lifestyle intervention mode, then it will have accomplished an enormous amount for the health of the country,” Dr. Genuth said.

Dr. Buse believes that identifying more patients with IFG may even help physicians in the long run.

“If anything, this should make it easier. As there will be more people in this boat, it may be easier to find more lay captains who will help encourage people to row,” he said.

Heidi Splete
Senior Writer

WASHINGTON — The epidemic growth of diabetes has prompted the Department of Health and Human Services to recommend screening all overweight people at age 45 for “prediabetes” and to consider screening younger, at-risk people.

This recommendation means that millions of Americans are now considered appropriate candidates for screening with fasting plasma glucose or oral glucose tolerance tests. (See chart .)

The announcement, made by HHS Secretary Tommy G. Thompson at a press briefing, is the product of a joint research panel of HHS, the American Diabetes Association, the National Institutes of Health, and the Centers for Disease Control and Prevention.

Patients with a fasting plasma glucose level between 110 and 125 mg/dL or a 2-hour oral glucose tolerance test value of 140-199 mg/dL should be considered at increased risk for developing type 2 diabetes. HHS is promoting diabetes testing as part of routine medical visits, although reimbursement issues remain to be worked out.

With no intervention, most people with elevated glucose levels develop type 2 diabetes within a decade, Secretary Thompson said. This pronouncement in support of early intervention is based on the finding of the Diabetes Prevention Program in which adults in the prediabetes category underwent modest lifestyle changes—diet and exercise—that reduced their risk of developing type 2 diabetes by more than 50%, compared with a control group (N. Engl. J. Med. 346[6]:393-403, 2001).

“Patients with prediabetes should be told that they have a serious condition, one that they can reverse with diet and exercise,” Dr. Judith Fradkin of NIH said at the press conference. “With these changes, many patients can actually restore their blood glucose levels to normal.”

The changes are modest—cutting calories and fat and walking 30 minutes per day 5 days per week—but even that is a challenge for many high-risk patients. HHS plans to endorse community support programs and a national program to spread the prevention message. “Every year a person can live free of diabetes is a year free of pain, disability, and medical costs,” Secretary Thompson said.

The HHS guidelines state that patients aged 45 years or older with normal fasting plasma glucose levels or normal results on oral glucose tolerance tests should be retested every 3 years. Those with glucose in the prediabetes range should be counseled on diet and exercise and be retested every 1-2 years to avert progression to frank diabetes.

Patients with a prediabetes diagnosis need to know that their clock is ticking. If allowed to progress to diabetes, they could be at risk for blindness, kidney failure, and other complications within the next 10-20 years.

The term prediabetes is more understandable to the general public, and is being preferred to the term impaired glucose tolerance, Dr. Gerald Bernstein explained in an interview.

Getting to the issues of exercise and nutrition early are important, he said. “People with impaired glucose tolerance are at risk and in need of intervention, and they are at extraordinary risk for cardiovascular disease whether or not they ever develop diabetes.”

Success at diet and exercise, however, is fraught with difficulties. Even the Diabetes Prevention Program participants, who were tightly supervised and encouraged in their healthy behaviors, were not uniformly compliant with the regimen.

Though not part of the HHS guidelines and not approved by the Food and Drug Administration for the indication, drug intervention with metformin can also reduce progression from prediabetes to clinical diabetes in patients if diet and exercise aren't stabilizing glucose levels, Dr. Bernstein said. Metformin therapy was a component of the Diabetes Prevention Program study, but its success was not superior to diet and exercise.

Dr. Bernstein, past president of the American Diabetes Association, said that he considered the results of oral glucose tolerance testing to be superior to those of a fasting glucose blood test. Both are good indicators, said Dr. Bernstein, now the vice president for medical affairs at Generex Biotechnologies in Toronto and a senior endocrinologist at Beth Israel Medical Center in New York. These interventions are “going to be expensive, but in the long run, they are cheaper than having people develop diabetes.”

For more information about the guidelines, check out www.diabetes.org.

Sources: Department of Health and Human Services and the American Diabetes Association