Diabetes mellitus is a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both. Type 2 diabetes, the most prevalent form of the disease, is often asymptomatic in its early stages and can remain undiagnosed for many years. Approximately 5.4 million adults in the U.S. have undiagnosed type 2 diabetes. The chronic hyperglycemia of diabetes is associated with long-term damage, dysfunction, and failure of various organs, especially the eyes, kidneys, nerves, heart, and blood vessels. Individuals with undiagnosed type 2 diabetes are at significantly higher risk for coronary heart disease, stroke, and peripheral vascular disease than the nondiabetic population. They also have a greater likelihood of having dyslipidemia, hypertension, and obesity.

Because early detection and prompt treatment may reduce the burden of type 2 diabetes and its complications, screening for diabetes may be appropriate under certain circumstances. This position statement provides recommendations for diabetes screenings performed in physicians' offices and community screening programs.

This position statement does not address screening for type 1 diabetes or gestational diabetes mellitus (GDM). Because of the acute onset of symptoms, most cases of type 1 diabetes are detected soon after symptoms develop. Widespread clinical testing of asymptomatic individuals for the presence of autoantibodies related to type 1 diabetes cannot be recommended at this time as the means to identify persons at risk. Reasons for this include the following: 1) cutoff values for some of the immune marker assays have not been completely established for clinical settings; 2) there is no consensus as to what action should be taken when a positive autoantibody test result is obtained; and 3) because the incidence of type 1 diabetes is low, testing of healthy children will identify only the small number (<0.5%) who at that moment may be "prediabetic." Clinical studies are being conducted to test various methods of preventing type 1 diabetes in high-risk subjects (e.g., siblings of type 1 patients). These studies may uncover an effective means of preventing type 1 diabetes, in which case screening may be appropriate in the future.

For information on screening for GDM, refer to the American Diabetes Association's position statement "Gestational Diabetes Mellitus."

DIABETES PREVALENCE AND RISK FACTORS
The prevalence of diagnosed and undiagnosed diabetes in adults in the U.S. is about 6%. However, specific subgroups have a much higher prevalence of the disease than the population as a whole. These subgroups have certain attributes or risk factors that either directly cause diabetes or are statistically associated with it.

The correlation of a risk factor(s) with development of diabetes is never 100%. However, the greater the number of risk factors present in an individual, the greater the chance of that individual developing or having diabetes. Conversely, the chance of finding diabetes in an individual without a risk factor is low. Thus, the likelihood of identifying an asymptomatic individual with diabetes in the general population through random screening is small; however, in high-risk groups the likelihood is much greater.

The risk of developing type 2 diabetes increases with age, obesity, and lack of physical activity. Type 2 diabetes is more common in individuals with a family history of the disease and in members of certain racial/ethnic groups. It occurs more frequently in women with prior GDM and in individuals with hypertension or dyslipidemia. Major risk factors for type 2 diabetes are summarized in Table 1.

SYMPTOMS
Symptoms of marked hyperglycemia include polyuria; polydipsia; weight loss, sometimes with polyphagia; and blurred vision. Assessment of the presence of individual symptoms has not proven to be a useful approach to population screening for diabetes. Also, type 2 diabetes frequently goes undiagnosed for many years because the hyperglycemia develops gradually, and thus the onset, and even the presence, of symptoms often goes unnoticed. Clearly, in a clinical setting, presence of symptoms, and particularly multiple symptoms, requires follow-up.

GENERAL RECOMMENDATIONS FOR SCREENING BY PHYSICIANS
Screening for diabetes as part of routine medical care may be appropriate if the patient has one or more of the risk factors shown in Table 1. Based on the lack of high-quality cost-benefit studies, it is premature to recommend screening all high-risk individuals. Thus, the decision to screen for diabetes should ultimately be based on clinical judgment and patient preference.

On the basis of expert opinion, screening of high-risk individuals should be considered at 3-year intervals. The rationale for this interval is that there is little likelihood of an individual developing diabetes and any of the complications of diabetes to a significant degree within 3 years of a negative screening test result.

Screening Tests
The fasting plasma glucose (FPG) test and the 75-g oral glucose tolerance test (OGTT) are both suitable tests for diabetes; however, the FPG test is strongly preferred because it is easier and faster to perform, more convenient and acceptable to patients, and less expensive. Fasting is defined as no consumption of food or beverage other than water for at least 8 h before testing.

An FPG level >126 mg/dl (7.0 mmol/l) or a 2-h postload value in the OGTT >200 mg/dl (11.1 mmol/l) are indications for retesting. Either test must be repeated on a different day to confirm a diagnosis. Table 2 presents the diagnostic criteria.

Table 2. Criteria for the Diagnosis of Diabetes Mellitus

Normoglycemia IFG or IGT DM* FPG <110 mg/dl 2-h PG <140 mg/dl FPG >110 and <126 mg/dl (IFG) 2-h PG>140 and <200 mg/dl (IGT) FPG >126 mg/dl 2-h PG>200 mg/dl Symptoms of DM and random plasma glucose concentration >200 mg/dl *A diagnosis of diabetes must be confirmed, on a subsequent day, by measurement of FPG, 2-h PG or random plasma glucose (if symptoms are present). The FPG test is greatly preferred because of ease of administration, convenience, acceptability to patients, and lower cost. Fasting is defined as no caloric intake for at least 8 h. This test requires the use of a glucose load containing the equivalent of 75 g anhydrous glucose dissolved in water. DM, diabetes mellitus; 2-h PG, 2-h postload glucose.

Nondiabetic individuals with an FPG >110 mg/dl (6.1 mmol/l) but <126 mg/dl (7.0 mmol/l) are considered to have impaired fasting glucose (IFG), and those with 2-h values in the OGTT >140 mg/dl (7.8 mmol/l) but <200 mg/dl (11.1 mmol/l) are defined as having impaired glucose tolerance (IGT). Both IFG and IGT are risk factors for future diabetes.

Normoglycemia is defined as plasma glucose levels <110 mg/dl (6.1 mmol/l) in the FPG and a 2-h postload value <140 mg/dl (7.8 mmol/l) in the OGTT.

If necessary, plasma glucose testing may be performed on individuals who have taken food or drink shortly before testing. Such tests are referred to as random plasma glucose measurements and are given without regard to time of last meal. A random plasma glucose level >160 mg/dl (8.9 mmol/l) is considered a positive screening test result. The diagnosis of diabetes is made on additional testing—preferably by the FPG test, or less preferably, by the OGTT—performed on subsequent days.

Laboratory measurement of plasma glucose concentration is performed on venous samples with enzymatic assay techniques, and the above-mentioned values are based on the use of such methods.

Glycated hemoglobin remains a valuable tool for monitoring glycemia, but it is not currently recommended for the screening or diagnosis of diabetes.

Other Considerations
In screening for disease, it is crucial that appropriate interpretation of the screening test results is provided to the patient and that follow-up evaluation and treatment are made available. Also, it is important to consider that certain drugs, including glucocorticoids, thiazides, estrogen-containing products, -blockers, and nicotinic acid, may produce hyperglycemia.

GENERAL RECOMMENDATIONS FOR COMMUNITY SCREENING PROGRAMS
The major objective of a community screening program is to identify individuals at high risk for having undiagnosed diabetes. To this end, a verbal or written questionnaire is recommended. The American Diabetes Association's diabetes risk test is shown in Fig. 1. This risk test has not been validated in individuals <20 years of age or in Asian Americans and Pacific Islanders. Because Asian Americans appear to develop diabetes at a lower BMI than other racial and ethnic groups, this risk test may underestimate their risk for undiagnosed diabetes.

Figure 1. American Diabetes Association's diabetes risk test.

Individuals who have been determined to be at risk should be referred to a physician for evaluation. In addition, individuals indicating that they have any diabetes symptoms should seek appropriate medical care. Community screening programs must have an established mechanism for referring individuals to a clinician for further evaluation.

Although there is ample scientific evidence showing that certain risk factors predispose individuals to development of diabetes (Table 1), there is insufficient evidence to conclude that community screening is a cost-effective approach to reduce the morbidity and mortality associated with diabetes in presumably healthy individuals. On the other hand, community screening programs clearly provide a means to enhance public awareness of the seriousness of diabetes and its complications. Thus, based on expert opinion, community screening for diabetes in high-risk populations may be worthwhile, but its true efficacy is unknown. In conclusion, to increase the cost-effectiveness of testing undiagnosed, otherwise healthy individuals, screening should be considered in high-risk populations. This recommendation is consistent with the "Report of the Expert Committee on the Diagnosis and Classification of Diabetes."

Use of GlycemicTesting in Community Screening Programs
If the community screening program is being implemented under the close supervision of a clinician, glycemic testing may be performed. Minors without consent, individuals with diagnosed diabetes, and pregnant women should not receive glycemic testing in community screening programs. Pregnant women should be referred to a physician for appropriate evaluation.

Criteria for Glycemic Testing in Community Screening Programs
Glycemic testing should be limited to individuals who have been found to be at high risk for having undiagnosed diabetes through the use of a verbal or written questionnaire (e.g., the Association's diabetes risk test).

Screening Tests
The screening test of choice is the FPG test. Fasting is defined as no consumption of food or beverage other than water for at least 8 h before testing. An FPG level >126 mg/dl (7.0 mmol/l) is an indication for evaluation by a physician.

Some screening programs use blood glucose monitoring devices (meters) approved by the Food and Drug Administration for home use. While testing of capillary blood glucose (e.g., finger-stick glucose) is not the recommended procedure, administrators of programs that use meters should practice regular quality-assurance procedures and be aware of manufacturers' recommendations regarding use of their specific testing devices. Many of these meters measure whole blood glucose and not plasma glucose. Note that plasma glucose values are 10–15% higher than whole blood glucose values.

Testing of capillary blood glucose should be done with the patient in the fasting state. Individuals with a fasting capillary whole blood glucose test result >110 mg/dl (6.1 mmol/l) should be referred to a physician for further testing. If necessary, a random test may be performed on individuals who have taken food or drink shortly before testing. An individual with a random capillary whole blood glucose test result >140 mg/dl (7.8 mmol/l) should be referred to a physician for further testing. Testing of blood with a blood glucose monitoring device intended for home use is not considered a diagnostic procedure, even if confirmed on another occasion. Thus, a screening test using whole blood glucose does not constitute the first test in the mandatory two-test procedure for diagnosing diabetes. Thus, a whole blood screening test must be confirmed two more times using plasma from a venous sample.

Table 3 defines glycemic test results that indicate additional testing and evaluation by a physician.

Other Considerations for Community Screening Programs

1.  Community screening programs must follow Occupational Safety and Health Administration guidelines.

2.  Personnel conducting screening programs must be adequately trained and demonstrate competency in the testing procedure used and in related program policies and procedures. The following topics should be included in a training program: