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ADA Consensus Statement: Oral Glucose Test Advised For ‘Prediabetes’ Screening

Apr 17, 2007

The new ADA consensus statement specifies that screening for prediabetes should involve the fasting plasma glucose test and the 2-hour oral glucose tolerance test and should be undertaken in the same population that is currently screened for diabetes.

Both tests must be done, on separate days, in order to confirm both impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT).


Recommended tests for the screening of patients who are at risk of developing type 2 diabetes may prove onerous for primary care providers.

These tests may present a burden in primary care settings, panel member Dr. Mayer B. Davidson noted in an interview. He cited a study showing that a random plasma glucose test was the method of diabetes screening used in 95% of 8,286 patients seen in a large HMO setting (Diabetes Care 2004;27:9–12).

“Very few people in the United States get an oral glucose tolerance test,” he commented.

The statement emphasizes lifestyle modification as key to management of IFG and/or IGT, however, metformin may be considered for patients who meet the criteria for both impairments, and who have at least one other risk factor, according to the ADA expert panel chaired by Dr. David M. Nathan, of Massachusetts General Hospital and Harvard University, both in Boston (Diabetes Care 2007;30:753–9).

This is the first ADA statement to offer off-label pharmacologic treatment for prediabetes.

Patients treated with metformin should be monitored with a hemoglobin A1c test semiannually, whereas those not on drug therapy should have annual office visits, according to the ADA statement.

“The overall message is that lifestyle is more important, even though it’s so much more difficult to get people to start it and maintain it,” Dr. Davidson said.

The ADA document notes that up to 70% of individuals with the “prediabetic” states of IFG (a fasting glucose of 100–125 mg/dL) or IGT (an oral glucose tolerance test with a 2-hour plasma glucose of 140–199 mg/dL) will eventually develop diabetes. The risk for cardiovascular disease is only moderately elevated with IFG and IGT, but that risk increases sharply with the onset of type 2 diabetes, along with diabetes-specific complications involving the eyes, nerves, and kidneys.

Increasing data in the last decade have shown that it is possible to prevent or delay the onset of type 2 diabetes using lifestyle modification, with or without medications. Strong evidence supports efforts to prevent or delay the onset of diabetes, although the evidence is conflicting as to whether such efforts will improve cardiovascular outcomes, Dr. Davidson said.
“To delay diabetes is to delay the risk for microvascular disease—this is known for sure. We don’t have enough evidence base to say that we’re preventing cardiovascular disease by preventing diabetes. But it’s possible, because we know that people who do get diabetes have a two- to fourfold increase in cardiovascular disease,” commented Dr. Davidson, professor of medicine at Charles R. Drew University and the University of California, Los Angeles.

The ADA document takes into account data from eight major clinical trials published between 1997 and 2006, all of which showed reductions in the development of diabetes, ranging from 25% to 60%.

The largest reductions (about 60%) were achieved in studies that tested lifestyle interventions aimed at a 5%–10% weight loss and moderate physical activity for about 30 minutes a day, and treatment with thiazolidinediones. Lesser degrees of reduction (about 25%–30%) were achieved with other medications.

On the basis of the available data, the panel recommended lifestyle modification alone for patients who have either IFG or IGT.

Metformin, 850 mg twice a day, may be added to the same lifestyle prescription for patients who have both IFG and IGT, as well as one or more of the following:

▸ Younger than 60 years of age.
▸ Body mass index of at least 35 kg/m2.
▸ Family history of diabetes in first-degree relatives.
▸ Elevated triglycerides.
▸ Reduced HDL cholesterol.
▸ Hemoglobin A1c greater than 6.0%.

The data supporting lifestyle intervention come primarily from two trials, the Diabetes Prevention Program (N. Engl. J. Med. 2002;346:393–403) and the Finnish Diabetes Prevention Study (N. Engl. J. Med. 2001;344:1343–50).

 “Our position has been that we should identify people at risk with insulin resistance and begin making lifestyle changes then, [rather than] wait until the patient has IFG or IGT,” said Dr. Hellman, clinical professor of medicine at the University of Missouri, Kansas City.

The ADA statement is a good one, although it doesn’t go far enough, said Dr. Hellman.

“It’s not particularly radical to say that a person with IGT would be put on metformin,” he said, noting that the progression from insulin resistance to IFG/IGT to diabetes is a continuous one. “We think there are probably more options where it would be appropriate than just the ones [the ADA included], but we think it’s a good first step.”