In December 2015, the United States Preventive Services Task Force updated its recommendation on screening for abnormal blood glucose and diabetes to say that clinicians should screen all adults ages 40 to 70 years who are overweight or obese as part of a cardiovascular risk assessment.1 This recommendation carries a B grade signifying a moderate certainty that a moderate net benefit will be gained by detecting impaired fasting glucose (IFG), impaired glucose tolerance (IGT), or diabetes, and by implementing intensive lifestyle interventions. In this article, as in the Task Force recommendation, the term diabetes means type 2 diabetes. Obesity is defined as a body mass index (BMI) of ≥30 kg/m2, and overweight as a BMI >25.
How the Task Force recommendation evolved
The previous Task Force recommendation on this topic, made in 2008, advised screening only adults with hypertension because there was no evidence that any other group benefited from screening. In subsequent years, there were calls for the Task Force to revise its recommendation to bring it more in line with that of the American Diabetes Association (ADA).2 While this new recommendation does add more adults to the cohort of those the Task Force believes should be screened, it is still not totally in concert with the ADA, which recommends screening all adults 45 years or older and those who are younger if they have multiple risk factors.3
Both the Task Force and the ADA acknowledge there is no direct evidence for any benefit in screening for diabetes in the general, asymptomatic population. The Task Force, with its standard of making recommendations only when good evidence supports them, has opted to address screening for abnormal glucose levels in the context of cardiovascular risk reduction and persuasive evidence that lifestyle interventions can reduce cardiovascular risks and slow progression to diabetes.
The ADA is willing to rely on less rigorous evidence of benefit in screening, diagnosing, and treating undetected diabetes. It believes that morbidity and mortality from this pervasive chronic disease can be reduced with early detection and treatment.
Still the Task Force and ADA agree more than they differ
While it appears that significant differences exist between the recommendations of the Task Force and the ADA, a closer look shows they actually have much in common; and, as they pertain to daily practice, any remaining differences are primarily ones of emphasis. For instance, the Clinical Considerations section of the Task Force recommendation acknowledges that certain people are at increased risk for diabetes at younger ages and at a lower BMI, and that clinicians should “consider” screening them earlier than at age 40 years. The risks listed include a family history of diabetes or a personal history of gestational diabetes or polycystic ovarian syndrome; or being African American, Hispanic, Asian American, American Indian, Alaskan Native, or Native Hawaiian.
The Task Force statement seems to imply—although this is not entirely clear—that those who have these risks should also be screened if they are older than age 40 years even if they are not obese. So, although the ADA would screen everyone ages 45 and older, the Task Force would screen everyone ages 40 and older, except for non-Hispanic whites who are not overweight or obese, and who have no other risk factors. TABLE 11,3 details the Task Force and the ADA screening criteria and how they differ.
The Task Force and the ADA also agree on the 3 tests acceptable for screening and the test values that define normal glucose, IGT, IFG, and diabetes (TABLE 2).1,3 The tests are a randomly measured glycated hemoglobin level, a fasting plasma glucose level, and an oral glucose tolerance test performed in the morning after an overnight fast, with glucose measured 2 hours after a 75-g oral glucose load. If a screening result is abnormal, confirmation should be sought by repeating the same test. And both organizations suggest that, following a normal test result, the optimal interval for retesting is 3 years.
Intervening to delay progression to diabetes
For anyone with a confirmed abnormal blood glucose level, the Task Force advises referral for intensive behavioral interventions—ie, multiple counseling sessions over an extended period on a healthy diet and optimal physical activity. These types of interventions can reduce blood glucose levels and lower the risk of progression to diabetes, and can help with lowering weight, blood pressure, and lipid levels. The evidence report that preceded the recommendation pooled the results from 10 studies on lifestyle modification.4 The length of follow-up in these studies ranged from 3 to 23 years, and the number needed to treat to prevent one case of progression to diabetes ranged from about 5 to 20.4