Minimal clinically important difference of the 6-min walking test in patients with asthma

BACKGROUND: The 6-min walking test (6MWT) is responsive to physiological changes and pulmonary rehabilitation (PR) in patients with asthma. The minimal clinically important difference (MCID) has not been established yet. OBJECTIVE: To determine the MCID of 6MWT in patients with asthma. METHODS: Using the perceived change in walking ability and the modified Medical Research Council (mMRC) score as anchors, receiver operating characteristic curves and quantile regression, we evaluated 6MWT before and after PR in these patients. The St George Respiratory Questionnaire (SGRQ), the COPD assessment test (CAT) and other outcome measures were also assessed. RESULTS: Of 142 patients with asthma, 37 were enrolled. After PR, 6MWT increased from 453.4 m +/- 88.8 to 493.0 m +/- 97.2 (P = 0.0001); other outcome measures also increased. There was a slight correlation between baseline 6MWT and SGRQ, CAT and mMRC. No significant correlations were found between post-PR changes in 6MWT and in other outcome measures. Comparing different methods of assessment, the MCID ranged from 26 m to 27 m. CONCLUSION: The most conservative estimate of the MCID of 6MWT after PR was 26 m in patients with asthma. This estimate may be useful in clinical interpretation of data, particularly in response to intervention studies.