Lung function impairment, COPD hospitalisations and subsequent mortality

Background Hospitalisations and their sequelae comprise key morbidities in the natural history of chronic obstructive pulmonary disease (COPD). A study was undertaken to examine the associations between lung function impairment and COPD hospitalisation, and COPD hospitalisation and mortality. Methods The analysis included a population-based sample of 20 571 participants with complete demographic, lung function, smoking, hospitalisation and mortality data, with 10-year median follow-up. Participants were classified by prebronchodilator lung function according to the modified Global Initiative on Obstructive Lung Disease (GOLD) criteria. Hospitalisations were defined by the presence of a COPD discharge diagnosis (ICD-9 codes 490-496). Incidence rate ratios (IRR) of COPD admissions and hazard ratios (HR) of mortality with respective 95% CI were calculated, adjusted for potential confounders. Results The prevalence of modified GOLD categories was normal (36%), restricted (15%), GOLD stage 0 (22%), GOLD stage 1 (13%), GOLD stage 2 (11%) and GOLD stages 3 or 4 (3%). Adjusted IRRs (and 95% CI) indicated an increased risk of COPD hospitalisation associated with each COPD stage relative to normal lung function: 4.7 (3.7 to 6.1), 2.1 (1.6 to 2.6), 3.2 (2.6 to 4.0), 8.0 (6.4 to 10.0) and 25.5 (19.5 to 33.4) for the restricted, GOLD stage 0, GOLD stage 1, GOLD stage 2 and GOLD stages 3 or 4, respectively. Hospitalisation for COPD increased the risk of subsequent mortality (HR 2.7, 95% CI 2.5 to 3.0), controlling for severity, number of prior hospitalisations and other potential confounders. The increase in mortality associated with admission was very similar across the modified GOLD stages. Conclusions COPD severity was associated with a higher rate of severe exacerbations requiring hospitalisation, although severe exacerbations at any stage were associated with a higher risk of short-term and long-term all-cause mortality.