Background: Asthma and COPD diagnoses are used to classify chronic airway diseases; however, both diseases are related to phenotypic traits like allergy, obesity, cough, sputum production, low-grade inflammation, smoking, elevated blood eosinophil count, comorbidities, and occupational exposures. Whether such traits can replace asthma and COPD diagnoses when assessing risk of exacerbation is unclear. We tested the hypothesis that individuals with either asthma or COPD diagnoses have similar risk of moderate and severe exacerbations when adjusted for differences in phenotypic traits.

Methods: From the Copenhagen General Population Study, a cohort study of the general population, we included 7190 individuals with chronic airway disease. Phenotypic traits were recorded at baseline and risk of exacerbations was assessed during follow-up from 2003 to 2013.

Results: The incidence rate ratio (IRR) of moderate exacerbations in individuals with clinical COPD was 1.61 (95% Confidence Interval, 1.27-2.02) compared to individuals with asthma in a model only adjusted for age, sex, and education, but after the inclusion of phenotypic traits IRR was 1.05 (0.82-1.35). Corresponding IRRs of severe exacerbations in individuals with clinical COPD versus asthma were 3.82 (2.73-5.35) and 2.28 (1.63-3.20), respectively.

Conclusions: When taking phenotypic traits into account, individuals with asthma and COPD had comparable risk of moderate exacerbations; however, corresponding risk of severe exacerbations was higher in individuals with COPD than in those with asthma.