Validation of the COPD Assessment Test (CAT) as an Outcome Measure in Bronchiectasis.

BACKGROUND: Objective assessment of symptoms in bronchiectasis is important for research and in clinical practice. The COPD Assessment Test (CAT) is a short, simple assessment tool widely used in COPD. The items included in the CAT are not specific to COPD and also reflect the dominant symptoms of bronchiectasis. We therefore performed a study to validate the CAT as an outcome measure in bronchiectasis.
METHODS: The CAT was administered to two cohorts of bronchiectasis patients along with other quality of life questionnaires. Patients underwent comprehensive clinical assessment. One cohort had repeated questionnaires collected before-and-after treatment of acute exacerbations. We analyzed convergent validity, repeatability, and responsiveness of the score and calculated the minimum clinically important difference (MCID) using a combination of distribution and anchor-based methods.
RESULTS: In both cohorts there were positive correlations between the CAT and the St. George's Respiratory Questionnaire (r = 0.90, P < .0001 and r = 0.87, P < .0001). There was an inverse relationship between CAT and Quality of Life - Bronchiectasis Respiratory Symptoms Scale (r = -0.75, P < .0001) and Leicester Cough Questionnaire score (r = -0.77, P < .0001). Patients with more severe disease, based on the bronchiectasis severity index, had significantly higher CAT scores. CAT also correlated with FEV1 % predicted and 6-min walk distance (6MWD). CAT increased significantly at exacerbation and fell at recovery. The intraclass correlation coefficient for two measurements four-weeks apart while clinically stable was 0.88 (95% CI, 0.73-0.95, P < .0001). An MCID of 4 was most consistent.
CONCLUSIONS: CAT is a valid, responsive symptom assessment tool in bronchiectasis. The MCID is estimated as 4 points.