Reproducibility of three six-minute walk tests in COPD patients referred for pulmonary rehabilitation

<bold>Rationale</bold> The six-minute walk test (6MWT) is used to assess functional capacity in COPD patients. Most patients tend to walk further in a second 6MWT. Research on further increasing the six-minute walk distance (6MWD) during a 3rd test has rarely been done. This study investigated 1) the reproducibility of three 6MWTs in COPD patients referred for pulmonary rehabilitation (PR) and 2) predictors of improvement in the 3^rd 6MWT. <bold>Methods</bold> 1167 COPD patients (50% male, age: 62±9 years; FEV₁: 42±18%pred) performed three 6MWTs (6MWT1, 6MWT2 and 6MWT3) pre-PR. An improvement in walking distance (6MWD) of ≥42m in consecutive 6MWTs was defined as improvement. Reproducibility was assessed using a Bland-Altman plot and logistic regression analyses were performed to assess effects of sex, age, BMI, GOLD-stage, 6MWD, use of supplemental O₂ and/or use of walking aids. <bold>Results</bold> Generally, the 6MWD improved (6MWT1: 343±115m; 6MWT2: 367±115m; 6MWT3: 381±116m). 210 patients (18%) improved ≥42m in 6MWT3 vs 6MWT2 (fig.1). The Bland-Altman plot showed that the 95% limits of agreement of 6MWT3 vs 6MWT2 exceeded 42m, indicating that 6MWT2 is not reproducible. Predictors of improvement in 6MWT3 were GOLD stage I/II and a low 6MWD in previous 6MWTs. <bold>Conclusion</bold> Three 6MWTs may be required to obtain the largest pre-PR functional capacity in COPD patients. Patients with a 6MWD <350m and GOLD-stage I/II are more likely to improve ≥42m in 6MWT3.