Estimating the prevalence of diabetes mellitus and thyroid disorders using medication data in Flanders, Belgium

Various methods exist to estimate disease prevalences. The aim of this study was to determine whether dispensed, self-reported and prescribed medication data could be used to estimate the prevalence of diabetes mellitus and thyroid disorders. Second, these pharmaco-epidemiological estimates were compared with prevalences based on self-reported diagnoses and doctor-registered diagnoses. Data on medication for diabetes and thyroid disorders were obtained from three different sources in Flanders (Belgium) for 2008: a purely administrative database containing data on dispensed medication, the Belgian National Health Interview Survey for self-reported medication and diagnoses, and a patient record database for prescribed medication and doctor-registered diagnoses. Prevalences were estimated based on medication data and compared with each other. Cross-tabulations of dispensed medication and self-reported diagnoses, and prescribed medication and doctor-registered diagnoses, were investigated. Prevalences based on dispensed medication were the highest (4.39 and 2.98% for diabetes and thyroid disorders, respectively). The lowest prevalences were found using prescribed medication (2.39 and 1.72%, respectively). Cross-tabulating dispensed medication and self-reported diagnoses yielded a moderate to high sensitivity for diabetes (90.4%) and thyroid disorders (77.5%), while prescribed medication showed a low sensitivity for doctor-registered diagnoses (56.5 and 43.6%, respectively). The specificity remained above 99% in all cases. This study was the first to perform cross-tabulations for disease prevalence estimates between different databases and within (sub)populations. Purely administrative database was shown to be a reliable source to estimate disease prevalence based on dispensed medication. Prevalence estimates based on prescribed or self-reported medication were shown to have important limitations.