title: Efficacy and effectiveness of screen and treat policies in prevention of type 2 diabetes: systematic review and meta-analysis of screening tests and interventions.
abstract: OBJECTIVE
  To assess diagnostic accuracy of screening tests for pre-diabetes and efficacy of interventions (lifestyle or metformin) in preventing onset of type 2 diabetes in people with pre-diabetes.
  
  
  METHODS
  Systematic review and meta-analysis.
  Medline, PreMedline, and Embase. Study protocols and seminal papers were citation-tracked in Google Scholar to identify definitive trials and additional publications. Data on study design, methods, and findings were extracted onto Excel spreadsheets; a 20% sample was checked by a second researcher. Data extracted for screening tests included diagnostic accuracy and population prevalence. Two meta-analyses were performed, one summarising accuracy of screening tests (with the oral glucose tolerance test as the standard) for identification of pre-diabetes, and the other assessing relative risk of progression to type 2 diabetes after either lifestyle intervention or treatment with metformin.
  
  
  METHODS
  Empirical studies evaluating accuracy of tests for identification of pre-diabetes. Interventions (randomised trials and interventional studies) with a control group in people identified through screening. No language restrictions.
  
  
  RESULTS
  2874 titles were scanned and 148 papers (covering 138 studies) reviewed in full. The final analysis included 49 studies of screening tests (five of which were prevalence studies) and 50 intervention trials. HbA1chad a mean sensitivity of 0.49 (95% confidence interval 0.40 to 0.58) and specificity of 0.79 (0.73 to 0.84), for identification of pre-diabetes, though different studies used different cut-off values. Fasting plasma glucose had a mean sensitivity of 0.25 (0.19 to 0.32) and specificity of 0.94 (0.92 to 0.96). Different measures of glycaemic abnormality identified different subpopulations (for example, 47% : of people with abnormal HbA1chad no other glycaemic abnormality). Lifestyle interventions were associated with a 36% (28% to 43%) reduction in relative risk of type 2 diabetes over six months to six years, attenuating to 20% (8% to 31%) at follow-up in the period after the trails.
  
  
  CONCLUSIONS
  HbA1cis neither sensitive nor specific for detecting pre-diabetes; fasting glucose is specific but not sensitive. Interventions in people classified through screening as having pre-diabetes have some efficacy in preventing or delaying onset of type 2 diabetes in trial populations. As screening is inaccurate, many people will receives an incorrect diagnosis and be referred on for interventions while others will be falsely reassured and not offered the intervention. These findings suggest that "screen and treat" policies alone are unlikely to have substantial impact on the worsening epidemic of type 2 diabetes.
  
  
  BACKGROUND
  PROSPERO (No CRD42016042920).
authors.affiliation: Nuffield Department of Primary Care Health Sciences, Radcliffe Primary Care Building, Radcliffe Observatory Quarter, University of Oxford, Oxford OX2 6GG, UK Eleanor.barry@phc.ox.ac.uk.
authors.forename: Eleanor
authors.initials: E
authors.lastname: Barry
authors.affiliation: Nuffield Department of Primary Care Health Sciences, Radcliffe Primary Care Building, Radcliffe Observatory Quarter, University of Oxford, Oxford OX2 6GG, UK.
authors.forename: Samantha
authors.initials: S
authors.lastname: Roberts
authors.affiliation: Nuffield Department of Primary Care Health Sciences, Radcliffe Primary Care Building, Radcliffe Observatory Quarter, University of Oxford, Oxford OX2 6GG, UK.
authors.forename: Jason
authors.initials: J
authors.lastname: Oke
authors.affiliation: Department of Diabetes, Newham University Hospital, Barts Health NHS Trust, London, UK.
authors.forename: Shanti
authors.initials: S
authors.lastname: Vijayaraghavan
authors.affiliation: Population Health Research Institute, St George's University of London, London SW17 0RE, UK.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Normansell
authors.affiliation: Nuffield Department of Primary Care Health Sciences, Radcliffe Primary Care Building, Radcliffe Observatory Quarter, University of Oxford, Oxford OX2 6GG, UK.
authors.forename: Trisha
authors.initials: T
authors.lastname: Greenhalgh
mesh_terms: D015415:Biomarkers / Q000032:analysis; D001786:Blood Glucose / Q000032:analysis; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000175:diagnosis / Q000517:prevention & control*; D005951:Glucose Tolerance Test; D006442:Glycated Hemoglobin / Q000032:analysis; D006801:Humans; D007004:Hypoglycemic Agents / Q000627:therapeutic use*; D008019:Life Style; D008403:Mass Screening / Q000379:methods* / Q000592:standards; D008687:Metformin / Q000627:therapeutic use*; D011236:Prediabetic State / Q000175:diagnosis / Q000628:therapy; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; D001786:Blood Glucose; D006442:Glycated Hemoglobin; D007004:Hypoglycemic Agents; D008687:Metformin