'Screen and Treat' Alone Unlikely to Prevent Type 2 Diabetes

Marcia Frellick

January 05, 2017

"Screen and treat," one of two strategies for preventing type 2 diabetes, is unlikely on its own to have much of an impact, according to a meta-analysis published online January 4 in the BMJ.

That approach, promoted by the United Kingdom's National Diabetes Prevention Programme and programs in the United States and Australia, among others, identifies those at high risk for diabetes individually and leads to treatment with metformin or lifestyle intervention.

The alternate strategy is a population-based approach where everyone is targeted through public-health policies, such as changes to transportation and use of green spaces.

Eleanor Barry, MBBS, of the Nuffield Department of Primary Care Health Sciences at University of Oxford in the United Kingdom, and colleagues, analyzed 46 studies of screening tests and 50 intervention trials.

They did two meta-analyses — one to study the accuracy of screening tests (compared with the oral glucose tolerance test) in identifying prediabetes and another to assess relative risk of developing diabetes after lifestyle interventions or metformin.

They found that the screenings (measuring HbA1c levels and fasting plasma glucose) were poor predictors of whether someone would develop type 2 diabetes and could lead to false confidence or unnecessary treatments.

HbA1c was ineffective both at predicting people at high risk (sensitivity levels of 49%) or low risk for diabetes (specificity 79%).

Fasting plasma glucose had a mean sensitivity of 25% and specificity of 94%.

Lifestyle interventions spanning 3 to 6 years showed a 36% drop in relative risk of type 2 diabetes from 6 months to 6 years, which fell to 20% in follow-up studies. But the authors acknowledge: "We have only moderate to very low confidence in these estimates, however, because study quality was often low."

Patients using metformin saw a relative risk reduction of 26% while taking the drug.

In addition, the analysis found inconsistency internationally as to what constitutes prediabetes. The authors note that prediabetes numbers would double if researchers used the American Diabetes Association's (ADA) cutoffs rather than the World Health Organization (WHO) cutoffs.

WHO and the International Expert Committee recommend diagnosis of prediabetes for those with a fasting plasma glucose of 6.0 to 6.9 mmol/L and HbA1c of 42-47 mmol/mol (6.0–6.4%).

By contrast, the ADA uses a cutoff for fasting plasma glucose of 5.6 to 6.9 mmol/L or HbA1c of 39 to 47  mmol/mol (5.7–6.4%).

Dr Barry and colleagues conclude that screening tests are poor predictors, but interventions have some success in reducing progression to diabetes for those who have the drive and the social support to sustain the changes.

However, those numbers will be small, they acknowledge, so they recommend more research into populationwide interventions.

422 Million Adults Living With Diabetes

Finding the right prevention strategy is critical as the prevalence surges worldwide. The authors write that "422 million adults are living with diabetes, and the number expected to die from its complications is predicted to double between 2005 and 2030."

Looking at the United Kingdom alone, already 3.2 million people have been diagnosed with type 2 diabetes. By 2025, that number is expected to grow to 5 million, at a cost of £23.7 billion ($30.2 billion) to the National Health Service.

In an accompanying editorial, Norman Waugh, MBChB, professor of public-health medicine and health-technology assessment at Warwick Medical School, University of Warwick, Coventry, United Kingdom, suggests more studies on a different, nonfasting test, given that previous studies have found it accurate and cost-effective for screening in the general population.

"Given the imperfections of HbA1c and fasting plasma glucose, it is a pity that more research has not been done on the nonfasting 50-g glucose challenge test, much used in screening for gestational diabetes but rarely used in screening for type 2 diabetes or impaired glucose tolerance," he says.

He suggests a balance of screening and treating individuals and policies that encourage changing lifestyle and maintaining that change across whole populations, although he acknowledges adherence to lifestyle advice is low.

Policy changes can include taxing some foods and sugary drinks or separating bike lanes from traffic lanes, he says.

"Preventing or delaying type 2 diabetes requires effective measures to motivate the general population to protect their own health," Dr Waugh writes.

The study authors and Dr Waugh declare no relevant financial relationships.

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BMJ. Published online January 4, 2017. Article, Editorial

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