History of Asthma in Patients with Chronic Obstructive Pulmonary Disease. A Comparative Study of Economic Burden.

RATIONALE: A diagnosis of asthma is considered an independent risk factor for chronic obstructive pulmonary disease (COPD). However, little is known about health service use patterns in patients with COPD who have a history of asthma in comparison with those without such a history, especially regarding comorbid conditions.

OBJECTIVES: To estimate the excess costs of COPD in patients with a history of asthma (COPD+asthma) versus those with COPD without such a history (COPD-only); to estimate excess costs attributable to inpatient care, outpatient care, medications, and community care; and to estimate excess costs attributable to comorbid conditions.

METHODS: We used vital statistics, inpatient and outpatient encounters, filled prescription records, and community care data of patients in British Columbia, Canada, from 1997 to 2012 to create propensity score-matched COPD+asthma and COPD-only cohorts. We calculated and compared the excess medical costs (in 2012 Canadian dollars [$]) between the two groups on the basis of billing information. Comorbidities were ascertained from the inpatient and outpatient records and were classified on the basis of major categories of the International Classification of Diseases, 10th Revision.

MEASUREMENTS AND MAIN RESULTS: The final sample consisted of 22,565 individuals within each group (mean age at baseline, 67.9 yr; 57.0% female; average follow-up, 4.07 yr). Excess costs of COPD+asthma were $540.7 per patient-year (PY) (95% confidence interval [CI], $301.7-$779.8; P < 0.001). Costs of medications ($657.9/PY; P < 0.001) and outpatient services ($127.6/PY; P < 0.001) were higher in COPD+asthma, but costs of hospitalizations were lower (-$271.0/PY; P = 0.002). Community care costs in the two groups were similar (P = 0.257). The excess cost of respiratory-related conditions was $856.2/PY (P < 0.001), with $552.6/PY being due to respiratory-related medications (P < 0.001); costs of all other conditions combined were lower in COPD+asthma, mainly due to lower costs of cardiovascular diseases (-$201.8/PY; P < 0.001).

CONCLUSIONS: Patients with COPD with a previous history of asthma consume more health care resources than those with COPD alone, but there are important differences in cost components and costs attributable to comorbid conditions. Further research is required to examine whether the lower costs of cardiovascular disease in these patients is due to lower levels of related risk factors or to intrinsic differences in COPD phenotypes.