POPULATION PREVALENCE OF DIABETES: VALIDATION OF A CASE DEFINITION FROM HEALTH ADMINISTRATIVE DATA USING A POPULATION-BASED SURVEY AND HOME BLOOD GLUCOSE SAMPLING

Background: Previous validation studies of diabetes case definitions from health administrative data are scarce and have not systematically assessed undiagnosed diabetes. We aimed to determine the accuracy of a diabetes case definition (two physician claims or one hospitalization for diabetes, within a two-year period; Canadian National Diabetes Surveillance System, NDSS) using a systematic review of the published literature and by comparing cases identified from the Quebec health services administrative databases to those obtained from self-report, respectively. We also estimated the prevalence of physician-diagnosed diabetes by self-report in a health survey, and undiagnosed diabetes by measuring glucose levels on mailed-in capillary blood samples.Methods: For the systematic review, we searched Medline (from 1950) and Embase (from 1980) databases for relevant validation studies published through August 2012 (keywords: "diabetes mellitus", "administrative databases" and "validation studies"). Reviewers abstracted study data and assessed quality using standardized forms. As there was heterogeneity, a random-effects bivariate regression model was used to pool sensitivity and specificity estimates. To determine the accuracy of the NDSS case definition from the Quebec health services administrative databases, we obtained administrative data on a stratified random sample of 6,247 Quebec individuals (2009) whom we surveyed by telephone to query diabetes status and asked them to mail-in fasting capillary blood samples to a central laboratory for glucose testing. The NDSS case definition was compared with self-reported diabetes alone and with self-reported diabetes and/or elevated glucose level (≥7 mmol/l) for sensitivity, specificity, positive and negative predictive values, and statistical agreement. Population-level prevalence was estimated using the NDSS definition, corrected based on sensitivity and specificity estimates and sampling weights. In addition, we added the Quebec validation study to the meta-analysis and reported the final test properties of the NDSS case definition.Results: The search strategy identified 1423 abstracts among which 11 studies were deemed relevant and reviewed; 6 of these reported sensitivity and specificity allowing pooling in a meta-analysis. Compared to surveys or medical records, sensitivity was 82.3% (95%CI 75.8, 87.4) and specificity was 97.9% (95%CI 96.5, 98.8). NDSS-based diabetes cases obtained from the Quebec health administrative databases compared to self-report revealed a sensitivity of the NDSS case definition of 84.3% (95%CI 79.3, 88.5) and specificity of 97.9% (95%CI 97.4, 98.4). Compared to self-report combined with glucose testing, sensitivity was 58.2% (95%CI 52.2, 64.6) and specificity was 98.7% (95%CI 98.0, 99.3). Adjusted for sampling weights, physician-diagnosed diabetes prevalence in Quebec was 7.2% (95%CI 6.3, 8.0) and total diagnosed and undiagnosed diabetes prevalence was 13.4% (95%CI 11.7, 15.0). Conclusion: Including the Quebec study in an updated meta-analysis of…