Analyses of data quality in registries concerning diabetes mellitus--a comparison between a population based hospital discharge and an insulin prescription registry.

To evaluate the data quality in the Danish National Registry of Patients (DNRP) and the Prescription Registry in the country of Northern Jutland (487,000 inhabitants) concerning insulin dependent diabetes mellitus (IDDM) and insulin treated diabetes mellitus, a comparison between data in the two registries was made. From the Regional Hospital Registry in the County of Northern Jutland, containing discharge diagnoses from all admissions to hospitals in the county, we identified all patients with the IDDM diagnosis between 1987 and 1993. From the Regional Prescription Registry all insulin prescriptions taken up at pharmacies in the county in 1993 were identified. All persons were identified by their individual identification number (CPR-number), and a record linkage between the two data sources was made. The predictive value of an IDDM-registration in the DNRP was 96% and the corresponding completeness 91%. In the Prescription Registry the completeness was 96%. Both registries seem to be valuable study bases for epidemiological research in diabetes mellitus.