Summary of Recommendations and Evidence

The U.S. Preventive Services Task Force (USPSTF) recommends screening for type 2 diabetes mellitus in asymptomatic adults with sustained blood pressure (treated or untreated) greater than 135/80 mm Hg ( Online Table A). B recommendation.

The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for type 2 diabetes in asymptomatic adults with blood pressure of 135/80 mm Hg or lower ( Online Table A). I statement.

Rationale

Importance. The prevalence of type 2 diabetes in the United States is increasing. About 9 percent of U.S. adults currently have this disorder. Diabetes is a leading cause of blindness, renal disease, and amputation, and leads to increased mortality, primarily from cardiovascular events.

Detection. The USPSTF found convincing evidence that available screening tests accurately detect type 2 diabetes during an early, asymptomatic phase.

Benefits of detection and early treatment. In adults with sustained blood pressure greater than 135/80 mm Hg: The USPSTF found adequate evidence that lowering blood pressure below conventional target values in adults who have hypertension and diabetes reduces the incidence of cardiovascular events and cardiovascular mortality.

In adults with blood pressure 135/80 mm Hg or lower: The USPSTF found convincing evidence that intensive glycemic control in persons with clinically detected (as opposed to screening-detected) diabetes can reduce progression of microvascular disease. However, the benefits of tight glycemic control on microvascular clinical outcomes, such as severe visual impairment or end-stage renal disease, take years to become apparent. There is inadequate evidence that early diabetes control as a result of screening provides an incremental benefit for microvascular clinical outcomes compared with initiating treatment after clinical diagnosis.

There is inadequate evidence that tight glycemic control significantly reduces macro-vascular complications, such as myocardial infarction and stroke.

Harms of detection and early treatment. The USPSTF found adequate evidence that the short-term harms of screening for diabetes, such as anxiety, are small. However, the longer-term effects of labeling a large proportion of U.S. adults as abnormal are unknown.

USPSTF assessment. The USPSTF concludes that for adults with sustained blood pressure greater than 135/80 mm Hg, there is moderate certainty that the net benefit of screening for diabetes is substantial.

The USPSTF concludes that for adults with blood pressure 135/80 mm Hg or lower, evidence of the value of screening for diabetes is lacking, and the balance of benefits and harms cannot be determined.

Clinical Considerations

• Patient population. This recommendation concerns adults without symptoms of diabetes or evidence of possible diabetes complications. Symptoms of diabetes include polyuria, polydipsia, and polyphagia. Possible diabetes complications include nonhealing ulcers or infections, and established vascular disease (e.g., coronary artery disease, stroke, peripheral artery disease). Persons with these symptoms or conditions should be tested for diabetes.

• Suggestions for practice (I statement). In persons with blood pressure of 135/80 mm Hg or lower, screening may be considered on an individual basis if knowledge of diabetes status would help inform decisions about coronary heart disease (CHD) prevention strategies. These include assessment of CHD risk and subsequent consideration of lipid-lowering agents or aspirin.

For example, consider a patient for whom lipid-lowering treatment would be recommended if his or her 10-year CHD risk was 20 percent or greater (see risk assessment). If the patient's calculated risk was 17 percent without diabetes and greater than 20 percent with diabetes, then screening for diabetes would be useful in determining treatment. However, if the patient's calculated risk was 10 percent without diabetes and 15 percent with diabetes, then the screening test result would have no effect on the decision whether to use lipid-lowering treatment.

• Risk assessment. Blood pressure is an important predictor of complications of cardiovascular disease (CVD), including CHD and stroke, in persons with type 2 diabetes. Blood pressure measurement should be the first step in applying this recommendation. The examination of global CHD and stroke risk allows the physician to determine how aggressive treatment for CVD risk factors needs to be. In making this assessment, physicians should use any of several validated CHD risk assessment calculators, such as the one based on Framingham Heart Study data (http://hp2010.nhlbihin.net/atpiii/calculator.asp).

• Screening tests. Three tests have been used to screen for diabetes: fasting plasma glucose, two-hour postload plasma glucose, and A1C testing. Each has advantages and disadvantages. The American Diabetes Association (ADA) has recommended the fasting plasma glucose test for screening because it is easier and faster to perform, more convenient and acceptable to patients, and less expensive than other screening tests. The fasting plasma glucose test has more reproducible results than the two-hour postload plasma glucose test; less intra-individual variation; and similar predictive value for development of microvascular complications of diabetes. The ADA defines diabetes as a fasting plasma glucose level of 126 mg per dL (6.99 mmol per L) or greater, and recommends confirmation with a repeat screening test on a separate day, especially in persons with borderline results.

• Treatment of persons with sustained blood pressure of 135/80 mm Hg or greater. Blood pressure targets should be lower for persons who have type 2 diabetes than for those who do not. Lower blood pressure targets for persons with diabetes and high blood pressure reduce CVD events compared with higher targets. Attention to other risk factors for CVD, such as physical inactivity, lipid levels, diet, and obesity, is also important to decrease risk of CHD and to improve glucose control.

• Screening intervals. The optimal screening interval is not known. The ADA recommends a three-year interval on the basis of expert opinion.

• Other approaches to prevention. There is no evidence of benefit in health outcomes from screening for impaired glucose tolerance or impaired fasting glucose. However, intensive programs of lifestyle modification (e.g., diet, exercise, behavior) reduce the incidence of diabetes. Regardless of whether the physician and patient decide to screen for diabetes, all patients should eat a healthful diet, be active, and maintain a healthy weight. These behaviors have other benefits in addition to preventing or forestalling type 2 diabetes. The USPSTF recommends intensive interventions for persons who are obese who desire to lose weight. Population-based approaches to increasing physical activity and reducing obesity, as recommended by the Task Force on Community Preventive Services, should be supported.

• Useful resources. Evidence and USPSTF recommendations regarding blood pressure, diet, physical activity, and obesity are available at http://www.uspreventiveservicestaskforce.org/recommendations.htm. The reviews and recommendations for the Task Force on Community Preventive Services are available at http://www.thecommunityguide.org.