Miriam E. Tucker
A new position statement from the International Diabetes Federation advises using a 1-hour 75-g oral glucose tolerance test (OGTT) to improve identification of people at risk of developing type 2 diabetes.
“There are many, many people who may appear ‘normal’ if you use A1c or fasting glucose, but if you do a glucose tolerance test, they may have an abnormality after a glucose load…The 1-hour plasma glucose has been found to be a more sensitive biomarker for the earlier identification of these high-risk individuals,” lead author Michael Bergman, MD, professor of medicine and population health at New York University Grossman School of Medicine, New York City, told Medscape Medical News in an interview.
Bergman presented the document, written by a 22-member international expert panel, on March 6, 2024, at the annual Advanced Technologies & Treatments for Diabetes meeting. It was simultaneously published in Diabetes Research and Clinical Practice.
This is the International Diabetes Federation’s (IDF’s) proposed screening algorithm for “intermediate hyperglycemia” and type 2 diabetes:
At-risk high-risk individuals are first screened with a validated questionnaire such as the FINDRISK or the American Diabetes Association’s (ADA’s) risk screening tool.
People identified as high risk should undergo laboratory screening with a 1-hour 75-g OGTT (although a 2-hour OGTT, fasting glucose, or A1c, as currently recommended by several organizations, is still considered acceptable).
People with a 1-hour plasma glucose value at or above 155 mg (8.6 mmol/L) are considered to have intermediate hyperglycemia and should be prescribed lifestyle intervention and referred to a diabetes prevention program.
Those with a 1-hour value greater than or equal to 209 mg/dL (11.6 mmol/L) are considered to have type 2 diabetes and should have a repeat test to confirm the diagnosis, with referral for further evaluation and treatment.
The new guidance is based on increasing evidence that the 1-hour test is a better predictor than other tests, including the 2-hour OGTT, of progression to type 2 diabetes and its associated complications, in a variety of populations. The document cites data showing that a plasma glucose of 155 mg/dl or greater on the 1-hour post-75-g test can identify people with undiagnosed type 2 diabetes or who are at increased risk but who have “normal” glucose tolerance as defined by an A1c < 5.7% (38.8 mmol/mol), a fasting plasma glucose < 100 mg/dL (5.6 mmol/L), or a 2-hour value below 140 mg/dL (7.8 mmol/L).
However, even though a 1-hour test may be more convenient than the traditional 2-hour test, incorporating OGTT into busy clinical practice may still pose logistical problems and may not improve ultimate outcomes, Elizabeth Selvin, PhD, MPH, of the Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, told Medscape MedicalNews. “I worry that emphasizing a burdensome test is not going to improve diabetes screening or diabetes prevention. Doing more 1-hour glucose screening is not going to get more people into diabetes prevention programs.”
When an audience member raised the logistics concern during the session Q&A, Bergman replied, “It’s no different than recommending colonoscopy or a mammogram…I tell patients that we want to learn more about what is going on before we make a firm diagnosis…I’ve done more than a hundred 1-hour glucose tolerance tests and have not seen one patient who refused because of inconvenience. Everything depends on the way we discuss things with patients.”
Recommendation Based on Emerging Evidence
“Intermediate hyperglycemia” is the World Health Organization’s term to refer to either impaired fasting glucose (IFG) or impaired glucose tolerance (IGT). These conditions are often called “prediabetes,” especially in the United States, but that term has been controversial because not everyone with IFG and IGT will go on to develop type 2 diabetes, said Bergman, who is also director of the NYU Langone Diabetes Prevention Program.
“With ‘prediabetes’ you’re labeling someone with a disease they may not develop. It’s not normal, but it’s not diabetes, so it’s an intermediate state,” he explained.
The statement provides a detailed summary of the data from 19 studies supporting use of a 1-hour plasma glucose of ≥ 155 mg/dL (8.6 mmol/L) to diagnose intermediate hyperglycemia and type 2 diabetes, including links between that level of glycemia and worsened metabolic and atherogenic profiles, risk for microvascular and macrovascular complications and mortality, and identification of risks for obstructive sleep apnea, cystic fibrosis-related diabetes mellitus, fatty liver disease, and premature mortality.
One major problem with current testing, Bergman said, is that “there is a huge disconnect between A1c and glucose values…Only about 30% of individuals with an abnormal A1c will have an abnormal fasting glucose, and the inverse is also true. There’s a big mismatch between the two.”
Current guidelines suggest using both A1c and fasting glucose, but Bergman said that even then “you’re still missing about 20-30% who have IGT…Part of the problem is that the criteria we use for defining abnormal fasting and 2-hour levels are too high…140 [mg/dL] for the 2-hour is too high and 100 [mg/dL] fasting is too high…And that’s one of the reasons why many people progress to type 2 diabetes, because we’re using screening thresholds that are nonphysiologic.”
But Selvin disagrees, pointing to her own work showing that “using a combination of fasting glucose and A1c for screening does an excellent job at identifying high-risk individuals.”
She’s also unconvinced by other data cited in the paper. “I am deeply skeptical about 1-hour glucose being more prognostic than all other glycemic tests…Associations of glucose tests with incident diabetes are inherently a circular analysis since diabetes is defined by elevations in those same tests. It is helpful to look at progression of diabetes, but these analyses are not simple and doing them well, especially with head-to-head comparisons against different glycemic tests, is hard,” she said.
In her view, “lifestyle interventions and weight loss should be recommended in at-risk individuals, including those with overweight and obesity, hypertension, metabolic syndrome, etc., regardless of 1-hour glucose test results.”
She added, “If we want to prevent diabetes, we need to focus on preventing weight gain and obesity and managing cardiometabolic risk factors. Lifestyle interventions are not effective unless they are intensive and patients are highly adherent. We need to make lifestyle interventions available and affordable for patients. That is the big barrier. I don’t think more screening with 1-hour glucose is going to help.”
Bergman pointed out that the International Diabetes Federation represents more than 100 countries, including many that are middle- and low-income. “They need a simple, cost-effective tool for screening effectively. A1c is more expensive, and fasting glucose alone will underestimate disease prevalence. So, the IDF felt, after doing a fairly comprehensive due diligence, that the data warranted recommendation of the 1-hour glucose.”
He’s hoping other organizations like the ADA and the World Health Organization will sign on to bring this guidance into the primary care arena. Medscape Medical News reached out to ADA for comment, but their representative hadn’t responded by press time.
Bergman had no disclosures. Selvin was supported by the National Institutes of Health.
Miriam E. Tucker is a freelance journalist based in the Washington DC area. She is a regular contributor to Medscape, with other work appearing in the Washington Post, NPR’s Shots blog, and Diatribe. She is on X (formerly Twitter) @MiriamETucker.
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