Methods: In November, 2007, patients with persistent asthma were mailed a survey that included the ACT, the mAQLQ, and the AIS-6 and that captured a history of asthma exacerbations in the prior 12 months. Year 2008 asthma exacerbations (oral corticosteroid dispensings within 7 days of an asthma encounter) were captured from administrative data. An exploratory factor analysis was performed using questions of the three tools, and individual patient factor scores were calculated by adding their raw scores for questions that loaded significantly positively on that factor and subtracting raw scores that loaded significantly negatively on that factor.
Results: The survey was returned by 2,751 participants, with 2680 (97.4%) having complete results for all three tools. Of these patients, 40 % had an asthma exacerbation in the prior 12 months and 23.3 % subsequently experienced an exacerbation. Asthma control defined by each tool and a history of prior exacerbations were significantly related (p < 0.0001) to subsequent exacerbations above and beyond the risk conferred by prior exacerbations. When prior exacerbations were included in the model, the three impairment tools provided similar and overlapping information, such that only the mAQLQ entered the model. Factor analysis revealed three factors (symptoms, activity, and bother), which were each significantly associated (p < 0.0001) with subsequent asthma exacerbations. However, only the functional factor (which included questions regarding limitation of usual work or daily activities) was independently related to subsequent exacerbations.
Conclusions: Asthma impairment is significantly related to the subsequent risk of exacerbations, but the ACT, mAQLQ, and AIS-6 do not provide independent information from each other in this regard. Interference with activities is the primary subjective component of asthma impairment that is related to the subsequent risk of exacerbations, further emphasizing the need to capture and improve this aspect of the impact of asthma on patients.