Use of the General Practice Research Database (GPRD) for respiratory epidemiology: a comparison with the 4th Morbidity Survey in General Practice (MSGP4).

BACKGROUND: The General Practice Research Database (GPRD) covers over 6% of the population of England and Wales and holds data on diagnoses and prescribing from 1987 onwards. Most previous studies using the GPRD have concentrated on drug use and safety. A study was undertaken to assess the validity of using the GPRD for epidemiological research into respiratory diseases.
METHODS: Age-specific and sex-specific rates derived from the GPRD for 11 respiratory conditions were compared with patient consultation rates from the 4th Morbidity Survey in General Practice (MSGP4). Within the GPRD comparisons were made between patient diagnosis rates, patient prescription rates, and patient "prescription plus relevant diagnosis" rates for selected treatments.
RESULTS: There was good agreement between consultation rates in the MSGP4 and diagnosis or "prescription plus diagnosis" from the GPRD in terms of pattern and magnitude, except for "acute bronchitis or bronchiolitis" where the best comparison was the combination category of "chest infection" and/or "acute bronchitis or bronchiolitis". Within the GPRD, patient prescription rates for inhalers, tuberculosis or hayfever therapy showed little similarity with diagnosis only rates but a similarity was seen with the combination of "prescription plus diagnosis" which may be a better reflection of morbidity than diagnosis alone.
CONCLUSIONS: The GPRD appears to be valid for primary care epidemiological studies by comparison with MSGP4 and offers advantages in terms of large size, a longer time period covered, and ability to link prescriptions with diagnoses. However, careful interpretation is needed because not all consultations are recorded and the coding system used contains terms which do not directly map to ICD codes.