THE MINIMUM CLINICALLY IMPORTANT IMPROVEMENT FOR THE INCREMENTAL SHUTTLE WALKING TEST

Abstract

Singh SJ, Jones PW, Evans R, Morgan MDL Thorax. Published online first April 4, 2008; doi:10.1136/thx.2007.081208. Background: The Incremental Shuttle Walking Test (ISWT) is used to assess exercise capacity in chronic obstructive pulmonary disease (COPD) and is employed as an outcome measure for pulmonary rehabilitation. This study was designed to establish the minimum clinically important difference (MCID) for the ISWT. Methods: Three hundred seventy-two patients (205 male) performed an ISWT before and after a 7 week outpatient pulmonary rehabilitation programme. After completing the course subjects were asked to identify, from a 5-point Likert scale, the perceived change in their exercise performance immediately upon completion of the ISWT. The scale ranged from “better” to “worse.” Results: The mean (SD) age was 69.4 (8.4) years, FEV1 1.06 (0.53) litres, and FEV1/FVC ratio 50.8 (18.1) %. Baseline shuttle walking test distance was 168.5 (14.6) m. After rehabilitation this increased to 234.7 (125.3) m. The mean difference and 95% confidence interval for the difference was 65.9 (58.9 to 72.9) m. For a subject to feel they were “slightly better” the mean improvement was 47.5 (38.6 to 56.5) m and to report feeling “better” the mean increase was 78.7 (70.5 to 86.9) m. Patients who reported that their exercise tolerance was “about the same” increased by a mean of 18.0 (4.5–31.5) m. Conclusion: Two levels of improvement were identified. The minimum clinically important improvement for the ISWT is 47.5m. In addition patients were able to distinguish an additional benefit at 78.7m. Editor's Comment. The ISWT has a greater following in the United Kingdom and other parts of Europe than in North America. It is a useful measure of real-life functional exercise capacity, but unlike the 6-minute walk test (6MWT), it was lacking in validated MCID data to allow it to be useful in longitudinal assessment. This lack of data has now been rectified by this study, which reports a generally expected relationship between perceived improvement, using a 5-point Likert scale, and ISWT distance. The most important of the presented results is the observation that for patients to feel even “slightly improved,” a mean 47.5 m improvement was required; this value is very close to the MCID reported for the 6MWT, and this concordance makes it likely that the results are robust, especially because the 6MWT data have been arrived at by different techniques and have remained reliably valid over 2 decades. The second observation that a mean increase of 78.7 m translated into patients feeling “better” is also useful but provides a less definitive threshold point than the MCID. Importantly, the baseline degree of effort limitation did not alter the MCID, similar to observations with the 6MWT. SK