Evaluation of the chronic obstructive pulmonary disease assessment test for measurement of health-related quality of life in patients with interstitial lung disease

Background and objective: A well-validated instrument that is simple to use is needed to assess health-related quality of life in patients with interstitial lung disease (ILD). The COPD assessment test (CAT) is a recently introduced, short and simple questionnaire for COPD patients, which shows good and valid measurement properties. This study was conducted to evaluate the validity of the CAT in patients with ILD. Methods: Patients with ILD (n = 55) completed the CAT and the St. George's Respiratory Questionnaire (SGRQ). These patients also completed the Medical Research Council (MRC) dyspnoea scale, the Leicester Cough Questionnaire (LCQ), and the hospital anxiety and depression scale; performed 6-min walk tests and pulmonary function tests; and provided samples for arterial blood gas analysis. Results: There was a very strong correlation between the CAT score and the SGRQ total score (r = 0.93, P < 0.0001). The CAT score was also significantly correlated with the SGRQ symptoms score (r = 0.74, P < 0.0001), the SGRQ activity score (r = 0.87, P < 0.0001) and the SGRQ impact score (r = 0.89, P < 0.0001). Stepwise multiple regression analysis demonstrated that the MRC and LCQ scores contributed most to both the CAT score and the SGRQ total score. Conclusions: The CAT is a short and simple questionnaire that shows good and valid measurement properties for assessing the health status of patients with ILD.