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Screening for type 2 diabetes and population mortality over 10 years (ADDITION-Cambridge): a cluster-randomised controlled trial
The Lancet, Early Online Publication, 4 October 2012
The increasing prevalence of type 2 diabetes poses a major public health challenge. Population-based screening and early treatment for type 2 diabetes could reduce this growing burden. However, uncertainty persists around the benefits of screening for type 2 diabetes. We assessed the effect of a population-based stepwise screening programme on mortality.
In a pragmatic parallel group, cluster-randomised trial, 33 general practices in eastern England were randomly assigned by the method of minimisation in an unbalanced design to: screening followed by intensive multifactorial treatment for people diagnosed with diabetes (n=15); screening plus routine care of diabetes according to national guidelines (n=13); and a no-screening control group (n=5). The study population consisted of 20 184 individuals aged 40—69 years (mean 58 years), at high risk of prevalent undiagnosed diabetes, on the basis of a previously validated risk score. In screening practices, individuals were invited to a stepwise programme including random capillary blood glucose and glycated haemoglobin (HbA1c) tests, a fasting capillary blood glucose test, and a confirmatory oral glucose tolerance test. The primary outcome was all-cause mortality. All participants were flagged for mortality surveillance by the England and Wales Office of National Statistics. Analysis was by intention-to-screen and compared all-cause mortality rates between screening and control groups. This study is registered, number ISRCTN86769081.
Of 16 047 high-risk individuals in screening practices, 15 089 (94%) were invited for screening during 2001—06, 11 737 (73%) attended, and 466 (3%) were diagnosed with diabetes. 4137 control individuals were followed up. During 184 057 person-years of follow up (median duration 9·6 years [IQR 8·9—9·9]), there were 1532 deaths in the screening practices and 377 in control practices (mortality hazard ratio [HR] 1·06, 95% CI 0·90—1·25). We noted no significant reduction in cardiovascular (HR 1·02, 95% CI 0·75—1·38), cancer (1·08, 0·901·30), or diabetes-related mortality (1·26, 0·75—2·10) associated with invitation to screening.
In this large UK sample, screening for type 2 diabetes in patients at increased risk was not associated with a reduction in all-cause, cardiovascular, or diabetes-related mortality within 10 years. The benefits of screening might be smaller than expected and restricted to individuals with detectable disease.
COMMENT: This study asks as many questions as it answers. The fundamental question is, of course, why such negative results? There are several conceivable answers we need to await additional analysis to determine the answer to this fundamental question: were the results negative because the population was a low risk and they needed little cardiovascular risk reduction< were they negative because the two most important cardiovascular risk factors, hypertension and hyperlipidemia, were treated equally well in both groups? Either would be good news. However, suppose the negative results were because cardiovascular risk factors were equally poorly controlled in both groups. We await further information.