Background:

Diabetes poses a tremendous and increasing clinical and public health burden for Americans; 19.3 million Americans over the age of 20 years are affected, one third of whom are undiagnosed.

Purpose:

To examine the evidence of the potential benefits and harms of screening adults for type 2 diabetes mellitus (DM2) and prediabetes in primary care settings in the United States.

Data Sources:

We searched Medline and the Cochrane Library for reviews and relevant studies published in English between March, 2001 and July, 2007.

Study Selection:

Studies of any design which examined the effects of a DM2 screening program on long-term health outcomes were included. Randomized controlled trials (RCTs) examining the effects of treatments for DM2 in persons with disease duration ≤ 1 year and prediabetes treatment studies were also included, as were RCTs where treatment effects were compared between persons with diabetes and normoglycemia.

Data Extraction:

Data were abstracted by one author and checked by a second. Key studies were reviewed and discussed by all authors.

Results:

There were no RCTs examining the effectiveness of a DM2 screening program. A small, case-control study did not suggest a benefit from screening when microvascular complications were considered. No study directly compared treatment effects between screen-detected and clinically-detected diabetic persons, nor have studies to date reported treatment effects in a screen-detected cohort with diabetes. Modeling studies suggest that screening for DM2 may be relatively cost-effective when macrovascular benefits of optimal blood pressure control are taken into account.

There was no clear evidence that persons with DM2 detected by screening would respond differently to specific antihypertensive regimens compared to persons without diabetes, and persons with diabetes and no known cardiovascular disease benefit from aggressive lipid control to a similar extent as persons without diabetes, but with known cardiovascular disease. In two new studies, aspirin did not appear to reduce the risk of myocardial infarction in DM2, but may lower the risk of ischemic stroke in women. There were no new data examining glycemic control strategies in persons with newly-diagnosed DM2.

Intensive lifestyle and various pharmacotherapeutic interventions decrease the incidence of DM2 over follow-up periods up to 7 years. There were little data, however, on the prevention or delay of cardiovascular and other long-term health outcomes, including death. Limited data from observational studies suggest no serious adverse effects of receiving a diagnosis of DM2 from screening. Recent systematic reviews of the adverse effects of drugs used in the treatment of DM2 and prediabetes do not reveal significant new data on harms.

Limitations:

Direct trial evidence of the benefits or harms of screening is lacking, therefore we relied solely on indirect evidence. Since the natural history of prediabetes and DM2 is not well elucidated, it remains unclear as to how applicable data from persons with DM2 ≤ 1 year is to screen-detected persons. Most of the treatment data are from subgroup analyses of large trials, which may be underpowered to address the comparisons of interest. The prediabetes studies had limited power and an insufficient length of follow-up to determine health outcomes in prediabetic persons.

Conclusions:

There is no direct trial evidence of the effectiveness of screening for DM2 or prediabetes. Data from the prior US Preventive Services Task Force review lead to recommendations that persons with DM2 with hypertension or hyperlipidemia benefit from screening for DM2; we identified few additional, relevant studies. There is evidence that lifestyle and pharmacotherapy can delay the progression of DM2 among persons with prediabetes, but little direct evidence that identifying persons with prediabetes will lead to long-term health benefits, although longer-term follow-up of these trials has yet to be completed.