Excess medical costs in patients with asthma and the role of comorbidity.

Asthmatic patients frequently have comorbidities, but the role of comorbidities in the economic burden of asthma is unclear. We examined the excess direct medical costs, including asthma- and comorbidity-related costs, in patients with asthma.We created a propensity score-matched cohort of patients newly diagnosed with asthma and non-asthmatic comparison subjects, both aged 5-55 years, from health administrative data (1997-2012) in British Columbia, Canada. Health services use records were categorised into 16 major disease categories based on International Classification of Diseases codes. Excess costs (in 2013 Canadian dollars ($)) were estimated as the adjusted difference in direct medical costs between the two groups.Average overall excess costs were estimated at $1058/person-year (95% CI 1006-1110), of which $134 (95% CI 132-136) was attributable to asthma and $689 (95% CI 649-730) to major comorbidity classes. Psychiatric disorders were the largest component of excess comorbidity costs, followed by digestive disorders, diseases of the nervous system, and respiratory diseases other than asthma. Comorbidity-attributable excess costs greatly increased with age but did not increase over the time course of asthma.These findings suggest that both asthma and comorbidity-related outcomes should be considered in formulating evidence-based policies and guidelines for asthma management.