THE UNIVERSITY OF BRITISH COLUMBIA
PURPOSE: To examine the effect of comorbidities on health-related quality of life (HRQoL) and their interaction with asthma control. METHODS: In a random sample of adults with asthma, we measured generic (EQ5D) and disease-specific (AQ5D) utility scores. Asthma symptom control was determined using the 2014 Global Initiative for Asthma Management Strategy. Comorbidity scores were calculated using a validated questionnaire. We used two-part regression models to measure the adjusted difference in utility across levels of symptom control and comorbidity scores and to examine the relative role of symptom control and comorbidity in explaining the variation in HRQoL. RESULTS: A total of 2,299 observations from 460 adult patients (mean age 52 years, 67 % women) were included. Compared to controlled asthma, uncontrolled asthma was associated with -0.018 reduction (95 % CI -0.028, -0.009) in EQ5D and -0.076 reduction (95 % CI -0.115, -0.052) in AQ5D utilities. An increase by one standard deviation in comorbidity score relative to the mean was associated with a change of -0.029 (95 % CI -0.043, -0.016) in EQ5D and -0.010 (95 % CI -0.020, -0.004) in AQLQ utilities. The impact of comorbidity was greater than asthma symptom control in explaining EQ5D variance (12 vs. 1 %) but smaller in explaining AQ5D variance (3 vs. 12 %). CONCLUSIONS: Generic and disease-specific HRQoL instruments differentially capture the impact of symptom control and comorbidity in asthma. The selection of HRQoL instruments for asthma studies should depend on the prevalence of comorbidity in the target population and the impact of interventions on asthma control and comorbidity.