New Draft Guidelines for Impaired Glucose Tolerance Screening

The United States Preventive Services Task Force (USPSTF) has released draft guidelines for type 2 diabetes mellitus (T2DM) screening.¹ The last guideline update on screening for T2DM in adults was published by the USPSTF in 2008.²

This update was based, in part, on an evidence review by the Agency for Healthcare Research and Quality (AHRQ) and Pacific Northwest Evidence-based Practice Center (EPC). Investigators evaluated the effects of screening in enabling earlier detection, earlier treatment, and aggressive initial treatment to improve long-term clinical outcomes in patients with impaired fasting glucose or impaired glucose tolerance.³

To evaluate the benefits and potential harms of screening for T2DM, AHRQ and EPC investigators searched the Cochrane Database for systematic reviews and randomized-controlled trials. Of these trials, 2 new studies of good or fair quality were identified to inform new recommendations: a study published in 2012 by Simmons et al in The Lancet,⁴ and another study published in 2014 by Li et al in the journal The Lancet: Diabetes & Endocrinology.⁵

Simmons et al evaluated outcomes in a long-term population mortality study known by the acronym ADDITION-Cambridge. In this study, investigators assessed the effect of a T2DM screening program over 10 years. Of 33 general physicians in eastern England, 15 were assigned to initiate intensive treatment for patients with diabetes, 13 were assigned to a screening intervention and routine care, and a third group of 5 physicians served as a control group. Investigators measured all-cause mortality in association with these 3 different interventions administered to 20,184 patients with a mean age was 58 years. After a median of 9.6 years, no significant difference in all-cause was observed in practices with intensive screening practices versus usual-care practices (HR: 1.06, 95% CI: 0.90-1.25). Results of a smaller, but longer-term study conflict with these results.⁴

In this smaller study—the Da Qing Diabetes Prevention Study—Li et al assessed outcomes in 33 clinics in China assigned 577 patients with impaired glucose tolerance equally to 4 groups: to usual therapy (control), diet, exercise, or both diet and exercise. In this 23-year follow-up of the original study, which was initiated in 1986, investigators assessed cardiovascular mortality, all-cause mortality, and the incidence of T2DM. Follow-up data were obtained for 99% of the original participants, and mortality data were obtained for 94% of the original participants. Compared with the control group, patients in intervention groups were⁵:

• 41% less likely to experience cardiovascular mortality (11.9% versus 19.6%; P = .033),
• 29% less likely to die of any cause (28.1% versus 38.4%; P = .049), and
• 45% less likely to develop T2DM (72.6% versus 89.9%; P = .001).

Based on these studies, the USPSTF issued a draft recommendation advocating screening for abnormal blood glucose levels and T2DM in adults who are at increased risk for diabetes as determined by presence of risk factors.¹

The 2008 guideline recommended screening for impaired glucose tolerance or impaired fasting glucose levels in patients with a blood pressure level >135/80 mm Hg, and found insufficient evidence to recommend such screening for patients with blood pressure levels of 135/80 mm Hg or lower.²

Under the draft guidance document, risk factors for developing T2DM noted by the USPSTF in the draft recommendation include¹:

• Older age (45 years or older)
• Being overweight or obese
• Having a first-degree relative with diabetes
• Having a history of gestational diabetes or polycystic ovarian syndrome (women only)
• Having ancestors of certain ethnic groups, including ancestors of African American, American Indian/Alaska Native, Asian American, Hispanic/Latino, or Pacific Island Native/Native Hawaiian descent

Several screening tests are available^1,6:

• The oral glucose tolerance test (OGTT), which involves measuring blood glucose levels 2 hour after administration of a 75-g oral glucose load during a fasting state (in the morning)
• A random plasma glucose level
• A fasting glucose level
• A random glycosylated hemoglobin level (HbA1C)

Importantly, at least 2 abnormal levels are needed to confirm a diagnosis of impaired fasting glucose or impaired glucose tolerance. Levels indicating impaired fasting glucose or impaired glucose tolerance are shown in Figure 1.^1,6

Figure 1: Definitions of Impaired Fasting Glucose or Impaired Glucose Tolerance

Test

Level Qualifying as Impaired Fasting Glucose or Impaired Glucose Tolerance

HbA1C level

5.7% to 6.4%

Random glucose level

140 to 199 mg/dL

Fasting glucose level

100 to 125 mg/dL

OGTT

140 to 199 mg/dL

HbA1C = glycosylated hemoglobin; OGTT = oral glucose tolerance test.

The USPSTF recommends interventions such as diet and exercise for patients with modifiable risk factors, including¹:

• High body mass index (including the categories overweight or obese categories)
• High blood pressure
• A sedentary lifestyle
• Lipid level abnormalities
• Smoking

Although the draft USPSTF recommendations do not note any specific medication interventions for preventing T2DM, the provisional recommendations do note that evidence exists supporting use of 3 medication classes that may delay the onset of T2DM¹:

• Biguanides (ie, metformin)
• Thiazolidinediones
• Alpha-glucosidase inhibitors

These draft recommendations from the USPSTF may enable detection of diabetes in the estimated 86 million adults in the United States with undiagnosed impaired fasting glucose or impaired glucose tolerance. With enhanced screening, more patients may reap the long-term benefits of lifestyle interventions and preventive medication. The public comment period on the draft recommendation expires on November 3, 2014. To comment on these draft screening recommendations, please visit the comment page on the USPSTF website.

References:

1. USPSTF. Draft recommendation statement: abnormal glucose and type 2 diabetes mellitus in adults: screening. www.uspreventiveservicestaskforce.org/Page/Document/RecommendationStatementDraft/screening-for-abnormal-glucose-and-type-2-diabetes-mellitus. Accessed October 2014.

2. USPSTF. Final recommendation statement diabetes mellitus (type 2) in adults: screening. http://www.uspreventiveservicestaskforce.org/Page/Document/RecommendationStatementFinal/diabetes-mellitus-type-2-in-adults-screening. Accessed October 2014.

3. Selph S, Dana T, Blazina I, Bougatsos C, Patel H, Chou R. Screening for type 2 diabetes mellitus: systematic review to update the 2008 U.S. Preventive Services Task Force

recommendation. Evidence synthesis no. 117. AHRQ Publication No. 13-05190-EF-1. Rockville, MD: Agency for Healthcare Research and Quality; 2014.

4. Simmons RK, Echouffo-Tcheugui JB, Sharp SJ, et al. Screening for type 2 diabetes and population mortality over 10 years (ADDITION-Cambridge): a cluster-randomised controlled trial. Lancet. 2012;380(9855):1741-1748.

5. Li G, Zhang P, Wang J, et al. Cardiovascular mortality, all-cause mortality, and diabetes incidence after lifestyle intervention for people with impaired glucose tolerance in the Da Qing Diabetes Prevention Study: a 23-year follow-up study. Lancet Diabetes Endocrinol. 2014;2(6):474-480.

6. American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes Care. 2012;35(suppl 1):S64-S71.