The COPD assessment test: a systematic review.

The COPD assessment test (CAT) is a self-administered questionnaire that measures health-related quality of life. We aimed to systematically evaluate the literature for reliability, validity, responsiveness and minimum clinically important difference (MCID) of the CAT. Multiple databases were searched for studies analysing the psychometric properties of the CAT in adults with chronic obstructive pulmonary disease. Two reviewers independently screened, selected and extracted data, and assessed methodological quality of relevant studies using the COSMIN checklist. From 792 records identified, 36 studies were included. The number of participants ranged from 45 to 6469, mean age from 56 to 73 years, and mean forced expiratory volume in 1 s from 39% to 98% predicted. Internal consistency (reliability) was 0.85-0.98, and test-retest reliability was 0.80-0.96. Convergent and longitudinal validity using Pearson's correlation coefficient were: SGRQ-C 0.69-0.82 and 0.63, CCQ 0.68-0.78 and 0.60, and mMRC 0.29-0.61 and 0.20, respectively. Scores differed with GOLD stages, exacerbation and mMRC grades. Mean scores decreased with pulmonary rehabilitation (2.2-3 units) and increased at exacerbation onset (4.7 units). Only one study with adequate methodology reported an MCID of 2 units and 3.3-3.8 units using the anchor-based approach and distribution-based approach, respectively. Most studies had fair methodological quality. We conclude that the studies support the reliability and validity of the CAT and that the tool is responsive to interventions, although the MCID remains debatable.