Background: There is a need for a standardized, valid, and reliable instrument for quantifying exacerbations of COPD. The objective of this study was to identify symptom items that characterize COPD exacerbations to form a new patient diary for evaluating exacerbation frequency, severity, and duration.
Methods: Twenty-three symptom items identified from patient interviews were administered to 410 patients with COPD aged (mean ± SD) 65 ± 10 years with stable FEV(1) of 51% predicted ± 20% predicted and 1.8 ± 1.8 exacerbations in the preceding 12 months. A total of 222 patients had a physician-diagnosed exacerbation; 188 were stable. Item-level analyses (floor and ceiling effects, criterion keying, item-total correlation) were used in the first stage of item reduction. Further reduction was conducted using Rasch model and descriptive item analyses. Exploratory factor analysis was performed on the items that survived the exclusion process.
Results: No item behaved differently between stable and exacerbation conditions. One item was removed after item-level analysis, and eight were removed following Rasch analysis. Together, the surviving 14 items met the criteria for a unidimensional measure of exacerbation severity. Internal consistency (person separation index) was excellent at 0.92. Post hoc exploratory factor analysis revealed one dominant factor, with three domains (breathlessness, cough and sputum, and chest symptoms) that accounted for 68% of the variance.
Conclusions: An exacerbation appears to be a quantitative rather than qualitative change from the stable state. This analysis identified a range of symptoms that form a unidimensional construct of overall exacerbation severity. The 14 items identified form the Exacerbations of Chronic Pulmonary Disease Tool (EXACT), a daily diary for detecting and quantifying exacerbation severity in COPD.