• Steven D Nathan, Roland M du Bois, Carlo Albera, Williamson Z Bradford, Ulrich Costabel, Alex Kartashov, Paul W Noble, Steven A Sahn, Dominique Valeyre, Derek Weycker, and Talmadge E King.
• Inova Fairfax Hospital, 3300 Gallows Rd., Falls Church, VA 22042, USA. Electronic address: steven.nathan@inova.org.
• Respir Med. 2015 Jul 1; 109 (7): 914-22.

BackgroundThe 6-minute walk test distance (6MWD) has been shown to be a valid and responsive outcome measure in patients with idiopathic pulmonary fibrosis (IPF). The analyses were based, however, on a single phase 3 trial and require validation in an independent cohort.ObjectiveTo confirm the performance characteristics and estimates of minimal clinically important difference (MCID) of 6MWD in an independent cohort of patients with IPF.MethodsPatients randomized to placebo in the phase 3 CAPACITY trials who had a baseline 6MWD measurement were included in these analyses. The 6MWD and other functional parameters (lung function, dyspnea, and health-related quality of life) were measured at baseline and 24-week intervals. Validity and responsiveness were examined using Spearman correlation coefficients. The MCID was estimated using distribution- and anchor-based methods.ResultsThe analysis comprised 338 patients. Baseline 6MWD was significantly correlated with lung function measures, patient-reported outcomes, and quality-of-life measures (validity). Compared with baseline 6MWD, change in 6MWD (responsiveness) showed stronger correlations with change in lung function parameters and quality-of-life measures. Dyspnea measured by the University of California San Diego Shortness of Breath Questionnaire showed the strongest correlations with 6MWD (baseline: coefficient -0.35; 48-week change: coefficient -0.37; both p < 0.001). The distribution-based analyses of MCID using standard error of measurement yielded an MCID of 37 m, and distribution-based analyses by effect size resulted in 29.2 m. The MCID by anchor-based analysis using criterion referencing (health events of hospitalization or death) was 21.7 m.ConclusionsThe 6MWD is a valid and responsive clinical endpoint, which provides objective and clinically meaningful information regarding functional status and near-term prognosis. These results confirm previous findings in an independent cohort of patients with IPF.Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

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