6MWT reference values invalid over 10 m
medwireNews: Researchers have found that patients with chronic obstructive pulmonary disease (COPD) cover a significantly shorter distance when completing the 6-minute walk test (6MWT) over a 10 m course compared with a 30 m course.
The team, led by Emmylou Beekman (Maastricht University, the Netherlands), says that most existing references for the test are based on the 30 m course, and therefore cannot be applied to 10 m courses, which are more commonly used in the primary care or physiotherapy setting.
The researchers used a double-crossover design in which 45 patients with COPD twice completed both a 10 m and a 30 m 6MWT 7 days apart.
They found that all participants achieved a shorter 6MWT distance (6MWD) on the 10 m course than on the 30 m course, at a mean of 49.5 m less.
And when the team used existing reference equations (based on course distances of 20 m, 30 m, 45 m, and 50 m) to predict the distance the participants would cover, they found that they overestimated the 6MWD on the 10 m course by 30% to 33%.
And, owing to the shorter distance covered on the 10 m course, % predicted values were on average 8% lower compared with those for the 30 m course.
“This overestimation results in a worse representation of a COPD patient’s functional exercise capacity,” comment the authors in the Journal of Physiotherapy.
“Moreover, achieving a 6MWD of less than 82% of the predicted value can be considered abnormal, which may influence the patient’s treatment plan.”
The team also notes that, as the average difference in 6MWD between the two tests, at 49.5m, is substantially greater than the minimal clinically important difference (MCID) of 25–35 m, this gives particular cause for concern and reason to believe that the difference is of practical relevance.
According to Beekman and colleagues, this research indicates that results of a 6MWT obtained using a 10 m course in primary care cannot be compared with those achieved on a 30 m course at a hospital. Furthermore, their findings have implications for research, highlighting the importance of course-length standardization across multicenter trials.
They conclude: “A subsequent step in research should be the development of related 6MWT thresholds for predicting morbidity and mortality and a MCID for the 6MWT on a 10 m course.”
medwireNews (www.medwirenews.com) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013
By Kirsty Oswald, medwireNews Reporter