title: The effect of varying the screening interval on false positives and duration of undiagnosed disease in a screening programme for type 2 diabetes.
abstract: OBJECTIVE
  The aims of this study were to quantify the proportion of people diagnosed as having type 2 diabetes by standard 75 g oral glucose tolerance test, in a hypothetical screening programme, who would actually be false positives (false positive percentage), and the effect on the false positive percentage of varying the time between repeat screens. We also calculated the duration in person years of exposure to undiagnosed disease in the population for each screening interval.
  
  
  METHODS
  Ely, Cambridgeshire, UK.
  
  
  METHODS
  We used the glucose tolerance data from 965 participants of the Ely Diabetes Project, who were tested 4.5 years apart, to calculate the population's between and within person variance for 2 hour plasma glucose, and constructed a probability matrix of observed v true glucose tolerance categories. The progression of the population between glucose tolerance categories was modelled assuming exponential times to progression.
  
  
  RESULTS
  After one year, 47.5% of test positives were disease free: almost half of those labelled with diabetes would not have the disease. For a 5 year interval, the false positive percentage was 27.6%, but the population would have been exposed to undiagnosed diabetes for 144 person years.
  
  
  CONCLUSIONS
  Screening can be associated with both benefit and harm; the balance is dependent on characteristics of the disease and the screening programme. This study has quantified the trade off between exposure to undiagnosed diabetes and false positive results to inform the debate about screening for type 2 diabetes.
authors.affiliation: Department of Primary Care and Public Health, University of Cambridge, UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Park
authors.forename: S J
authors.initials: SJ
authors.lastname: Griffin
authors.forename: S W
authors.initials: SW
authors.lastname: Duffy
authors.forename: N J
authors.initials: NJ
authors.lastname: Wareham
mesh_terms: D001786:Blood Glucose / Q000378:metabolism; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology; D018450:Disease Progression; D004739:England; D005189:False Positive Reactions; D018149:Glucose Intolerance / Q000175:diagnosis* / Q000453:epidemiology; D005951:Glucose Tolerance Test; D006801:Humans; D008403:Mass Screening; D015233:Models, Statistical; D011336:Probability; D012016:Reference Values; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: D001786:Blood Glucose