Comparison of CAT and CCQ in a clinical COPD population

Background: The COPD Assessment Test (CAT) and the Clinical COPD Questionnaire (CCQ) are both clinically useful health status instruments. We investigated how well the two instruments correlate, and if factors influencing CAT and CCQ differ. Methods: CAT and CCQ forms were completed by 432 randomly selected primary and secondary care patients with a clinical COPD diagnosis. Correlation analysis of CAT and CCQ was performed. Linear regression established the association between CCQ and CAT. To allow comparison of factors influencing the instruments, standardised scores were created for the CAT and CCQ scores. Separate multiple linear regression analyses for CAT and CCQ examined associations with sex, age (≤ and >65 years), exacerbations (≥1 vs 0 previous year), body mass index (BMI), heart disease, anxiety/depression and forced expiratory volume in one second as percentage of predicted (FEV1%pred, subgroup with n=246). Results: CAT and CCQ correlated well (r=0.88, p <0.0001), as did CAT ≥10 and CCQ ≥1 (r=0.78, p<0.0001). CCQ 1.0 corresponded to CAT 9.93 and CAT 10 to CCQ 1.29. Both instruments were associated with BMI <20 (standardised adjusted regression coefficient (95%CI) for CAT 0.53 (0.16 to 0.90) and CCQ 0.57 (0.21 to 0.93)), exacerbations (CAT 0.33 (0.26 to 0.41) and CCQ 0.37 (0.30 to 0.44)), heart disease (CAT 0.39 (0.18 to 0.59) and CCQ 0.26 (0.06 to 0.46)), anxiety/depression (CAT 0.38 (0.17 to 0.58) and CCQ 0.43 (0.23 to 0.63)) and FEV1%pred (CAT -0.008 (-0.013 to -0.003) and CCQ -0.009 (-0.014 to -0.004)). Conclusion: CAT and CCQ correlate well with each other. Heart disease, anxiety/depression, underweight, exacerbations, and low lung function are associated with worse health status assessed by both instruments.