• COPD epidemiology
• COPD exacerbations

In times of fiscal restrictions, health services need to invest resources where they will give the best return. Reducing hospital admissions by investing in improved disease management in the community is a prime target for those trying to save money.1 In their paper on the association of population and primary healthcare factors with hospital admissions for chronic obstructive pulmonary disease (COPD), Calderón-Larrañaga et al2 have shone an overdue spotlight on the determinants of admission rates. The authors have integrated routinely collected data sources on a breathtaking scale, using data from over 8000 practices caring for over 53 million people in England. They report a dramatic variation in admission rates from 125 to 646 per 100 000 of population, which demands an explanation.

Among population factors, smoking rates and deprivation were unsurprisingly associated with higher prevalence and admission rates. The prevalence of undiagnosed COPD was also found to be an important contributor. To calculate undiagnosed prevalence it was necessary to estimate the expected prevalence rate using a mathematical model and to subtract the diagnosed prevalence determined by primary care disease registers. Several problems arise from this approach. Among others, disease registers are inaccurate—in one study 27% of those on COPD registers did not meet the spirometric criteria for COPD.3 Furthermore, the mathematical model was based on deprivation according to post codes, a process which may underestimate deprivation in practice populations.4

Various explanations can be postulated as to why the undiagnosed prevalence may affect admission rates. For instance, undiagnosed patients are likely to be denied interventions which might prevent admissions. On the other hand, a high undiagnosed prevalence rate may simply reflect a high disease burden due to …