The reliability of hospital and pharmaceutical data to assess prevalent cases of chronic obstructive pulmonary disease.

Identifying chronic obstructive disease (COPD) cases is required to estimate COPD prevalence, to enroll COPD cohorts and to estimate air pollution health effects. Administrative health data are frequently used to identify COPD cases, though their validity has not been satisfactorily assessed. This paper aims to assess the contribution of pharmaceutical data in detecting COPD cases and to estimate the reliability of hospital/mortality databases in detecting COPD cases. Prevalent COPD cases among 35-plus-year-olds were estimated in four Italian areas in 2006 from hospital/mortality registries and adding pharmaceutical data. Age-specific and age-standardized prevalence rates were calculated in each area. Internal validity of COPD diagnoses from hospital and mortality databases was assessed. Pharmaceutical database was used to confirm the hospital/mortality COPD cases and to examine the selection and misclassification of hospitalized cases. Possible misclassification between COPD and asthma cases was estimated using hospital data. Prevalent COPD cases were 77,098 from hospital/mortality registries, 172,357 when respiratory prescriptions were added. Prevalence ranged from 4.0%-6.7%. Only 22.7% of pharmaceutical COPD cases were hospitalized or died and only 37.2% of hospital/mortality cases consumed respiratory medicines; this last proportion increased to 64.5% among the older cases with a principal diagnosis. COPD cases with a contemporary asthma diagnosis were 3.1%. We found that pharmaceutical data increases COPD prevalence estimates 2.2-2.5 times. Hospitalization does not necessarily indicate COPD severity, COPD as a principal diagnosis confirmed with medicine prescription more likely represented true cases. Misclassification affects asthma cases to greater extent than COPD cases.