Validation and comparison of reference equations for the six-minute walk test

¹ Bay Pines VA Health Care System, USA
² Hospital Universitario Nuestra señora de la Candelaria, Spain
³ Hospital Miguel Servet, Zaragoza, Spain
⁴ Universidad de Montevideo, Uruguay
⁵ St. Elizabeth's Medical Center, USA
⁶ Hospital Universitario de Caracas, Venezuela

^* To whom correspondence should be addressed. E-mail: claudia.cote{at}va.gov.

	Abstract

Exercise impairment as measured by the 6 minute walk test (6MWD) afflicts many patients with chronic obstructive pulmonary disease (COPD) and is known to predict mortality. Reference equations for the 6MWD in adults have been published but not yet validated.

We prospectively followed 1,379 patients with COPD for 55±30 months and tested the predictive value of the baseline 6MWD in meters, the 6MWD work (Kg·m^-1), and as percent of predicted by two reference equations: ENRIGHT et al., and TROOSTER et al. All cause mortality was the validating outcome. We identified the best threshold values for each of the tests using receiver operating curves (ROC). Results: The thresholds were: 350 meters for the 6MWD, 25,000 Kg·m^-1 for the 6MWDW, 67% predicted for Enright and co-workers and 54% predicted for TROOSTER et al. All modalities of the testing were similar at predicting COPD mortality and correlated well with the 6MWD test; Trooster % predicted (r=0.96, CI 0.95–0.96, p<0.0001), Enright % predicted (r=0.93, CI 0.92–0.94, p<0.0001) and 6MWDW (r=0.83, CI 0.81–0.85, p<0.0001).

We conclude that all modalities of testing predict mortality in COPD equally well. For the 6MWD test, a value lower than 350 meters is associated with increased mortality and should be regarded as abnormal.

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