Assessment of the under-reporting of diabetes in hospital admission data: a study from the Scottish Diabetes Research Network Epidemiology Group.

AIMS: Good quality data are required to plan and evaluate diabetes services and to assess progress against targets for reducing hospital admissions and bed days. The aim of this study was to assess the completeness of recording of diabetes in hospital admissions using recent national data for Scotland.
METHODS: Data derived from linkage of the Scottish National Diabetes Register and hospital admissions data were analysed to assess the completeness of coding of diabetes in hospital inpatient admissions between 2000 and 2007 for patients identified with diabetes prior to hospital admission.
RESULTS: In 2007, only 59% of hospital inpatient admissions for people previously diagnosed with diabetes mentioned diabetes, whereas over 99% of people with a mention of diabetes on hospital records were included in the diabetes register. The completeness of diabetes recording varied from 44 to 82% among mainland National Health Service Boards and from 34 to 89% among large general hospitals. Completeness of recording of diabetes as a co-morbidity also varied by primary diagnosis: 70 and 41% of admissions with coronary heart disease and cancer as the primary diagnosis mentioned co-existing diabetes, respectively.
CONCLUSIONS: There is wide variation in the completeness of recording of diabetes in hospital admission data. Hospital data alone considerably underestimate the number of admissions and bed days but overestimate length of stay for people with diabetes. Linkage of diabetes register data to hospital admissions data provides a more accurate source for measuring hospital admissions among people diagnosed with diabetes than hospital admissions data.