Minimal important difference and responsiveness of 2-minute walk test performance in people with COPD undergoing pulmonary rehabilitation.

BACKGROUND AND OBJECTIVES

Field exercise tests (eg, 6-minute walk test [6MWT]) are important measures of functional exercise capacity in people with COPD. Shorter tests such as the 2-minute walk test (2MWT) may offer advantages in some populations but lack information about responsiveness to change. This study examined responsiveness, minimal important difference (MID), test-retest reliability, and construct validity of the 2MWT in people with stable COPD attending outpatient pulmonary rehabilitation (PR).

METHODS

At pre-PR assessment, study participants completed a 2MWT twice in addition to usual measures (6MWT and Chronic Respiratory Questionnaire). At post-PR assessment following a standard PR program, measures were repeated and global rating of change scores obtained (patient and therapist). Pre-post program change scores were examined for correlations with change in 2-minute walk distance (2MWD) and used (where ≥0.3) to estimate the MID through anchor-based methods. Distribution-based estimates based on standard error of measurement were examined. Test-retest reliability (intraclass correlation coefficient [ICC] and Bland-Altman agreement) and validity (Pearson correlation with 6-minute walk distance [6MWD]) were reported.

RESULTS

Fifty-nine people (28 men) with stable COPD, mean age 68 years (SD 10 years), and percentage predicted forced expiratory volume in 1 second 48% (SD 20%) attended pre-PR assessment. Test-retest ICC for same-session 2MWD was 0.985. A mean difference of 2.4 m (95% confidence interval [CI] 0.7-4.0 m, =0.006) occurred between the first and second trials. 2MWD and 6MWD were highly correlated (=0.87, <0.001). Forty-one participants completed PR and were included in responsiveness and MID analysis. Mean 2MWD improved significantly post-PR (8.8 m, 95% CI 3.6-14 m, =0.001). The MID in 2MWD, anchored against clinically meaningful change in 6MWD, was 5.5 m (area under curve =0.81, =0.001). Distribution-based methods estimated an MID of 4 m.

CONCLUSION

Change in 2MWD of at least 5.5 m following a PR program corresponded to a clinically meaningful change. A practice test is recommended due to learning effects.