Increase in walk distance is not enough evidence to add a walk to the 6-minute walk test

From the authors:

H.S. Kulkarni and coworkers argue that a mean increase in 6-min walk distance (6MWD) of 27 m during a second 6-min walk test (6MWT) in 1,514 patients with chronic obstructive pulmonary disease (COPD) still does not provide enough evidence to consider performing two 6MWTs [1]. Even though we very much appreciate this correspondence, we disagree with the arguments and conclusions of H.S. Kulkarni and coworkers.

H.S. Kulkarni and coworkers state that we implied that only the result of the second 6MWT should be used. This is incorrect; we did not state this in our manuscript [1]. Indeed, 18% of the patients with COPD walked further during the first 6MWT. Moreover, the use of the best of two 6MWTs (defined as the best 6MWD) is very common in the COPD literature [2–5].

82% of our patients with COPD walked further during the second 6MWT. Indeed, the mean difference between the first and second 6MWT of 27 min is currently considered as clinically important in patients with moderate-to-very-severe COPD [6, 7]. Moreover, we verified, through the Bland–Altman analysis, that the limits of agreement between the first and second 6MWT largely exceed the upper limit of clinically important change [8]. Both findings support the implementation of a second 6MWT. Moreover, an improvement in 6MWD as a result of learning may be interpreted erroneously as a positive treatment; and the yearly change in 6MWD in COPD is estimated to be, on average, -26 m [9]. These are two additional strong arguments in favour of considering a second 6MWT.

H.S. Kulkarni and coworkers argue that the 6MWT should be compared with the outcomes of a cardiopulmonary cycling test, health status or symptoms. Nevertheless, the proposed outcomes may not be valid anchors for anchor-based minimal important difference estimates [10–12]. The argument of H.S. Kulkarni and coworkers that a second 6MWT is too expensive and requires too much effort seems invalid, as a 6MWT is simple and less time consuming than a formal cardiopulmonary exercise test. Moreover, we believe that the benefits of avoiding measurement error when assessing functional exercise capacity and prognosis in COPD are more relevant than the modest costs and effort required to perform a second 6MWT. In addition, reimbursement is arranged [13].

In conclusion, the 6MWT is a simple, easy and cheap test, with valuable clinical information, ignoring the fact 82% of the patients walk further during the second 6MWT can have clinical consequences, as discussed extensively in our article [1].

• ©ERS 2011