II. TESTING FOR PRE-DIABETES AND DIABETES IN ASYMPTOMATIC PATIENTS

Recommendations

• Testing to detect pre-diabetes and Type 2 diabetes in asymptomatic people should be considered in adults of any age who are overweight or obese (BMI ≥25 kg/m2) and who have one or more additional risk factors for diabetes. In those without these risk factors, testing should begin at age 45 years.
• If tests are normal, repeat testing should be carried out at least at 3-year intervals.
• To test for pre-diabetes or diabetes, an FPG test or 2-h OGTT (75-g glucose load) or both are appropriate.
• An OGTT may be considered in patients with IFG to better define the risk of diabetes.
• In those identified with pre-diabetes, identify and, if appropriate, treat other CVD risk factors.

For many illnesses, there is a major distinction between screening and diagnostic testing. However, for diabetes, the same tests would be used for “screening” as for diagnosis. Type 2 diabetes has a long asymptomatic phase and significant clinical risk markers. Diabetes may be identified anywhere along a spectrum of clinical scenarios ranging from a seemingly low-risk individual who happens to have glucose testing, to a higher-risk individual whom the provider tests because of high suspicion of diabetes, to the symptomatic patient. The discussion herein is primarily framed as testing for diabetes in those without symptoms. Testing for diabetes will also detect individuals with pre-diabetes.

A. Testing for pre-diabetes and Type 2 diabetes in adults

Type 2 diabetes is frequently not diagnosed until complications appear, and approximately one-third of all people with diabetes may be undiagnosed. Although the effectiveness of early identification of pre-diabetes and diabetes through mass testing of asymptomatic individuals has not been definitively proven (and rigorous trials to provide such proof are unlikely to occur), pre-diabetes and diabetes meet established criteria for conditions in which early detection is appropriate. Both conditions are common, increasing in prevalence, and impose significant public health burdens. There is a long presymptomatic phase before the diagnosis of Type 2 diabetes is usually made. Relatively simple tests are available to detect preclinical disease. Additionally, the duration of glycemic burden is a strong predictor of adverse outcomes, and effective interventions exist to prevent progression of pre-diabetes to diabetes (see Section IV) and to reduce risk of complications of diabetes (see Section VI).

Recommendations for testing for pre-diabetes and diabetes in asymptomatic:

Testing should be considered in adults of any age with BMI ≥25 kg/m2 and one or more risk factors for diabetes. Because age is a major risk factor for diabetes, testing of those without other risk factors should begin no later than age 45 years.

Either FPG testing or the 2-h OGTT is appropriate for testing. The 2-h OGTT identifies people with either IFG or IGT, and thus, more pre-diabetic people at increased risk for the development of diabetes and CVD. It should be noted that the two tests do not necessarily detect the same pre-diabetic individuals. The efficacy of interventions for primary prevention of Type 2 diabetes has primarily been demonstrated among individuals with IGT, not individuals with IFG (who do not also have IGT). As noted in the diagnosis section (Section I.B), the FPG test is more convenient, more reproducible, less costly, and easier to administer than the 2-h OGTT. An OGTT may be useful in patients with IFG to better define the risk of diabetes.

The appropriate interval between tests is not known. The rationale for the 3-year interval is that false-negatives will be repeated before substantial time elapses, and there is little likelihood that an individual will develop significant complications of diabetes within 3 years of a negative test result.

Because of the need for follow-up and discussion of abnormal results, testing should be carried out within the health care setting. Community screening outside a health care setting is not recommended because people with positive tests may not seek, or have access to, appropriate follow-up testing and care. Conversely, there may be failure to ensure appropriate repeat testing for individuals who test negative. Community screening may also be poorly targeted, i.e., it may fail to reach the groups most at risk and inappropriately test those at low risk (the worried well) or even those already diagnosed.

B. Testing for Type 2 diabetes in children

The incidence of Type 2 diabetes in adolescents has increased dramatically in the last decade, especially in minority populations, although the disease remains rare in the general adolescent population. Consistent with recommendations for adults, children and youth at increased risk for the presence or the development of Type 2 diabetes should be tested within the health care setting.

The recommendations of the ADA consensus statement on Type 2 diabetes in children and youth, with some modifications:

C. Screening for Type 1 diabetes

Generally, people with Type 1 diabetes present with acute symptoms of diabetes and markedly elevated blood glucose levels, and most cases are diagnosed soon after the onset of hyperglycemia. However, evidence from Type 1 prevention studies suggests that measurement of islet auto-antibodies identifies individuals who are at risk for developing Type 1 diabetes. Such testing may be appropriate in high-risk individuals, such as those with prior transient hyperglycemia or those who have relatives with Type 1 diabetes, in the context of clinical research studies. Widespread clinical testing of asymptomatic low-risk individuals cannot currently be recommended, as it would identify very few individuals in the general population who are at risk. Individuals who screen positive should be counseled about their risk of developing diabetes. Clinical studies are being conducted to test various methods of preventing Type 1 diabetes, or reversing early Type 1 diabetes, in those with evidence of autoimmunity.