Original article
Updating the Minimal Important Difference for Six-Minute Walk Distance in Patients With Chronic Obstructive Pulmonary Disease

https://doi.org/10.1016/j.apmr.2009.10.017Get rights and content

Abstract

Holland AE, Hill CJ, Rasekaba T, Lee A, Naughton MT, McDonald CF. Updating the minimal important difference for six-minute walk distance in patients with chronic obstructive pulmonary disease.

Objective

To establish the minimal important difference (MID) for the six-minute walk distance (6MWD) in persons with chronic obstructive pulmonary disease (COPD).

Design

Analysis of data from an observational study using distribution- and anchor-based methods to determine the MID in 6MWD.

Setting

Outpatient pulmonary rehabilitation program at 2 teaching hospitals.

Participants

Seventy-five patients with COPD (44 men) in a stable clinical state with mean age 70 years (SD 9y), forced expiratory volume in one second 52% (SD 21%) predicted and baseline walking distance 359 meters (SD 104m).

Interventions

Not applicable.

Main Outcome Measures

Participants completed the six-minute walk test before and after a 7-week pulmonary rehabilitation program. Participants and clinicians completed a global rating of change score while blinded to the change in 6MWD.

Results

The mean change in 6MWD in participants who reported themselves to be unchanged was 17.7 meters, compared with 60.2 meters in those who reported small change and 78.4 meters in those who reported substantial change (P=.004). Anchor-based methods identified an MID of 25 meters (95% confidence interval 20–61m). There was excellent agreement with distribution-based methods (25.5–26.5m, κ=.95). A change in 6MWD of 14% compared with baseline also represented a clinically important effect; this threshold was less sensitive than for absolute change (sensitivity .70 vs .85).

Conclusions

The MID for 6MWD in COPD is 25 meters. Absolute change in 6MWD is a more sensitive indicator than percentage change from baseline. These data support the use of 6MWD as a patient-important outcome in research and clinical practice.

Section snippets

Methods

Patients who were referred for pulmonary rehabilitation at 2 tertiary hospitals were invited to participate. Patients were eligible if they had a diagnosis of COPD confirmed on spirometry15 and were in a stable clinical state. Patients were excluded if they had comorbidities that prevented exercise training (severe cardiac or neurologic conditions, severe osteoarthritis). The study was approved by the human research ethics committees of both institutions.

Results

Seventy-nine participants were recruited; 4 participants did not complete the program and did not return for final assessment. Demographic characteristics of the 75 included participants (44 men) are in table 1. Ten participants had mild disease, 30 had moderate disease, 23 had severe disease, and 12 had very severe disease.23 There was a wide range of 6MWDs (104–523m).

Discussion

This study has shown that in patients with COPD and a wide range of disease severity, the MID for the 6MWD is approximately 25 meters. This result was consistent across anchor-based and distribution-based methods. A change in 6MWD of 14% of baseline walking distance may also be important to patients; however, this criterion is less sensitive. Patient and clinician estimates of clinically important change were similar.

This is the first study that we know of to prospectively evaluate the MID for

Conclusions

The MID for 6MWD in COPD is approximately 25 meters. A change in 6MWD of 14% also represents an important effect; however, this threshold is less sensitive than the absolute change in distance. The identification of an MID for 6MWD supports the continued use of the six-minute walk test to identify patient-important change in research and clinical practice.

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