The COPD assessment test and St George's Respiratory Questionnaire: are they equivalent in subjects with COPD?

Background: The chronic obstructive pulmonary disease (COPD) assessment test (CAT) is a short questionnaire that has facilitated health status measurements in subjects with COPD. However, it remains controversial as to whether the CAT can be used as a suitable substitute for the St George's Respiratory Questionnaire (SGRQ). This study investigated the reliability and score distributions of the CAT and SGRQ and evaluated which factors contributed to health status for each questionnaire. Methods: A total of 109 consecutive subjects with stable COPD from a single center were enrolled in this study. Each subject completed pulmonary function tests, exercise tests, and the following self-administered questionnaires: the Baseline Dyspnea Index, the Hospital Anxiety and Depression Scale, the CAT, and SGRQ. Results: Internal consistencies of CAT and SGRQ total scores were both excellent (Cronbach's alpha coefficients =0.890 and 0.933). Statistically significant correlations were observed between CAT and SGRQ total scores (R=0.668, P<0.001). Correlations of CAT scores with parameters related to pulmonary function, dyspnea, exercise performance, and psychological factors were inferior to correlations with those parameters with SGRQ total scores. Both multiple regression analyses and principal component analyses revealed that there were slight differences between SGRQ total scores and CAT scores. Conclusion: The CAT is similar to SGRQ in terms of discriminating health status. However, we demonstrated that what is assessed by the CAT may differ slightly from what is measured by SGRQ.