Rationale:

• Early recognition and aggressive treatment of risk factors for diabetes complications such as hypertension, hyperlipidemia, and hyperglycemia may delay or prevent common diabetes complications.
• Although there is no direct evidence that screening for type 2 diabetes improves health outcomes or mortality, there is good evidence that detecting diabetes improves estimates of cardiovascular risk and may provide an opportunity for earlier and more aggressive interventions (e.g., more aggressive hypertension and lipid control) to reduce cardiovascular events in patients with diabetes. However, it is not clear at this time whether screening is cost-effective.
• Ethnicity and the presence of certain comorbid diseases influence the prevalence of diabetes.
• Secondary causes of type 2 diabetes are rare and should be considered only when there are suggestive signs or symptoms.

Evidence:

• Type 2 diabetes often is present for at least 4 to 7 years before diagnosis (14).
• Cardiovascular disease is the most common complication of type 2 diabetes, and the benefits of screening are most apparent in patients with a high risk of cardiovascular disease (15; 16; 17).
• Because 15% to 30% of patients have evidence of early microvascular disease at the time of diagnosis (14; 18), screening and earlier detection of diabetes might reduce the risk of long-term complications (19), as might improving glycemic control through earlier diagnosis and treatment (20; 21; 22). However, this has not been tested in clinical trials and remains a theoretical benefit.
• Management of hypertension, use of lipid-lowering agents, and use of aspirin all have benefits in patients with type 2 diabetes (23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33).
• Epidemiologic data show the increased risk for diabetes in patients with a family history of type 2 diabetes, obesity, hypertension, personal history of gestational diabetes, membership in certain ethnic groups, and the presence of atherosclerotic disease (34; 35; 36; 37; 38; 39; 40; 41; 42).
• Assuming only once-in-a-lifetime screening and a long duration (10.5 years) of undiagnosed disease, a simulation model (43) has shown that the cost of screening patients under the age of 55, of any race, is comparable to that of many accepted medical interventions (<$50,000 per quality-adjusted life-year gained). However, once-in-a-lifetime screening in a young population has a low yield and is unlikely to be adopted in primary care. Overall this model does not provide much support for routine screening in the general population.
• The benefits of screening are likely to be confined to patients with treatable risk factors for cardiovascular disease such as hypertension and hyperlipidemia; however, screening a general population may not be effective or cost-effective (17).
• It is estimated that only a small proportion of cases (perhaps 1% to 2%, although there are few good studies) of type 2 diabetes are due to secondary cases, such as genetic disorders, medications, and other underlying diseases (44).

Comments:

• Screening for diabetes in the general population, although often advocated, has limited supporting evidence at this time. The benefits are theroretical and assume that early diagnosis leads to improved health care behaviors by patients and providers. The effect of screening for diabetes on health outcomes is an understudied area. However, the limited available data suggest that, even for a high-risk group such as blacks, screening is cost-effective only when done once and in those under age 55 (43).
• The simulation model constructed by the CDC is useful but has some major limitations. It assumed a particularly long duration of diabetes before diagnosis (10.5 years; most assume a 4- to 7-year duration of disease before diagnosis), and modeled only once-in-a-lifetime screening, an intervention unlikely to occur in the primary care setting (14). Further, it does not address the critical area of modifiable cardiovascular risk. The findings are not particularly convincing in terms of providing support for screening the general population.
• More study is needed on the costs and effectiveness of screening in high-risk groups.