Based on a review of the evidence, the task force recommends screening for prediabetes and type 2 diabetes in adults ages 35 to 70 who have overweight or obesity. The agency also recommends that clinicians offer or refer patients with prediabetes to effective preventive interventions. This is a “B” recommendation, and applies to nonpregnant adults seen in primary care settings who have overweight (defined as a BMI of 25 or greater) or obesity (defined as a BMI of 30 or greater) and no symptoms of diabetes.
“Clinicians can prevent serious health complications by screening adults with overweight or obesity for prediabetes and diabetes,” said task force member Chien-Wen Tseng, M.D., M.P.H., M.S.E.E., associate research director in the Department of Family Medicine and Community Health at the University of Hawaii John A. Burns School of Medicine, in a press release. “With appropriate screening, diabetes can be detected and treated earlier to improve overall health.”
Diabetes is the seventh leading cause of death in the United States, and the leading cause of kidney failure, adult blindness and lower-limb amputations. The American Diabetes Association estimates that in 2018, more than 34 million Americans, or roughly 10.5% of the population, had diabetes, and that in 2015, another 88 million Americans age 18 and older had prediabetes.
The final recommendation differs slightly from, and replaces, the task force’s October 2015 recommendation statement on screening for abnormal blood glucose and type 2 diabetes in asymptomatic adults.
In the 2015 recommendation, the USPSTF gave a “B” recommendation to screening for abnormal blood glucose as part of cardiovascular risk assessment in adults aged 40 to 70 years who are overweight or obese. The 2015 recommendation also stated that clinicians should offer or refer patients with abnormal blood glucose to intensive behavioral counseling interventions to promote a healthful diet and physical activity.
Although the AAFP supported the 2015 recommendation, the Academy also concluded at the time that there was inadequate evidence to determine whether early detection of abnormal blood glucose or diabetes led to improvements in mortality or cardiovascular morbidity.
To update the 2015 recommendation, the task force commissioned a systematic review that focused on direct evidence of the benefits and harms of screening for prediabetes and type 2 diabetes, and the benefits and harms of interventions for those with prediabetes or type 2 diabetes that was screen-detected or recently diagnosed for populations and settings relevant to primary care. The review also examined the evidence of effectiveness of interventions for prediabetes to delay or prevent progression to type 2 diabetes.
Data sources included studies and trial registries published through Sept. 10, 2019, along with reference lists of retrieved articles and data from outside experts and reviewers, with additional surveillance of the literature conducted through May 21, 2021. A total of 89 publications were included in the review.
The task force reviewed two randomized clinical trials that evaluated the effect of screening for diabetes on health outcomes. Compared with no screening, neither trial found a reduction in all-cause or type-specific mortality with screening over approximately 10 years of followup. In addition, neither trial found statistically significant differences in cardiovascular events, quality of life, nephropathy or neuropathy between screening and control groups, although data collection was limited to a minority of trial participants.
For individuals with screen-detected type 2 diabetes, results from one randomized clinical trial found no improvement in health outcomes over 5 to 10 years. An analysis of 38 trials that assessed the effects of behavioral or pharmacologic interventions for prediabetes found no statistically significant differences in all-cause mortality or cardiovascular events, and no or small improvements in quality-of-life scores.
For individuals with recently diagnosed type 2 diabetes that was not screen-detected, interventions such as intensive glucose control were associated with decreased risk of all-cause mortality, diabetes-related mortality and myocardial infarction over 10 to 20 years.
For individuals who were overweight or obese and had prediabetes, lifestyle interventions were associated with reduced incidence of progression to diabetes and improvements in intermediate outcomes such as weight reduction, systolic blood pressure and diastolic blood pressure. In addition, limited evidence suggested that high-contact lifestyle interventions improved health outcomes after more than 20 years.
Use of medications such as metformin, thiazolidinediones and alpha-glucosidase inhibitors was also found to reduce the incidence of diabetes, with the evidence for metformin considered consistent, precise and generally of good quality. However, the task force also stated in the evidence review that head-to-head trial data demonstrate that lifestyle interventions are superior to metformin in reducing diabetes incidence.
Evidence of harms associated with screening or interventions was limited.
A draft version of the recommendation statement was posted on the USPSTF website from March 16, 2021, to April 12, 2021.
In response to numerous comments, the task force clarified that disparities in prediabetes and type 2 diabetes prevalence are due to social factors, not biological factors, and incorporated person-first language when referring to patients who have overweight or obesity.
Several commenters requested that the task force broaden the eligibility criteria for screening to all adults, or to people with any risk factor for diabetes, and not just to those who have overweight or obesity. In response, the USPSTF stated that while it appreciates these perspectives, the available evidence best supports screening beginning at age 35 years. It also added clarifying language to indicate that overweight and obesity are the strongest risk factors for developing prediabetes and type 2 diabetes.
The USPSTF also noted, based on post-hoc analyses of Diabetes Prevention Program Study and Diabetes Prevention Program Outcomes Study, that metformin appears to be effective in reducing the risk of progression from prediabetes to diabetes in individuals with a history of gestational diabetes.
“This USPSTF recommendation has significantly expanded screening for diabetes,” said Sarah Coles, M.D., chair of the Academy’s Commission on Health of the Public and Science and an assistant professor in the Department of Family, Community and Preventive Medicine at the University of Arizona College of Medicine – Phoenix Family Medicine Residency.
Coles also noted that the task force’s decision to include screening for prediabetes — defined as an HbA1c level of 5.7% to 6.4% or a glucose level of 140 to 199 mg/dL following a two-hour glucose tolerance test — could be considered controversial.
“By lowering the screening age, a much larger population will be screened and ultimately labeled with diabetes or prediabetes, potentially also increasing the number of individuals on medication,” Coles explained. “Unfortunately, the belief that diabetes results from lack of self-control or poor choices persists in and out of healthcare settings. Genetics, social determinants of health and health equity play a much greater role in the development of diabetes and we must work tirelessly to reduce stigma, improve health outcomes, and empower our patients.”
Coles reminded FPs who screen for prediabetes that screening is neither sensitive nor specific; as such, screening could result in both false-positive and false-negative test results.
“Positive tests should be repeated before a diagnosis of prediabetes or impaired glucose tolerance is made,” said Coles. “Trials that looked at screening and treatment of individuals identified as having prediabetes have not shown improvement in important patient-oriented outcomes like morbidity or mortality. Because of the absence of patient-oriented benefits to screening, family physicians should discuss the risks and benefits of screening with their patients prior to ordering these tests.”
Fortunately, there are a number of preventive measures patients can take to either stop prediabetes or lessen its effects.
“Prediabetes is a risk factor for diabetes, and the goal is to prevent progression,” said Coles. Lifestyle interventions like diet and exercise are first-line to prevent progression to diabetes and have been shown to have short-term improvements in weight, blood pressure and cholesterol levels. These interventions would likely be indicated for this patient population, even without screening.”
Finally, Coles advised members who want additional information to visit the Academy’s Clinical Recommendations webpage, which contains information on diabetes and related topics, along with preventive services, clinical practice guidelines and Choosing Wisely recommendations.
In addition to the final recommendation statement, final evidence review and evidence summary, the task force provided links to several resources for clinicians and patients, including
The task force also noted that it has published additional recommendation statements on related topics, including screening for gestational diabetes and behavioral weight loss interventions to prevent obesity-related morbidity and mortality in adults.
The AAFP’s Commission on Health of the Public and Science plans to review the task force’s final recommendation statement, final evidence summary and evidence review, and will then determine the Academy’s stance on the recommendation, up to and including a revision of the Academy’s current recommendation.
Once the review is completed, members can visit the clinical preventive services recommendations section of the AAFP website for the latest recommendations.