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Six-minute-walk test in chronic obstructive pulmonary disease: minimal clinically important difference for death or hospitalization.

RATIONALE
Outcomes other than spirometry are required to assess nonbronchodilator therapies for chronic obstructive pulmonary disease. Estimates of the minimal clinically important difference for the 6-minute-walk distance (6MWD) have been derived from narrow cohorts using nonblinded intervention.


OBJECTIVES
To determine minimum clinically important difference for change in 6MWD over 1 year as a function of mortality and first hospitalization in an observational cohort of patients with COPD.


METHODS
Data from the ECLIPSE cohort were used (n = 2,112). Death or first hospitalization were index events; we measured change in 6MWD in the 12-month period before the event and related change in 6MWD to lung function and St. George's Respiratory Questionnaire (health status).


MEASUREMENT AND MAIN RESULTS
Of subjects with change in the 6MWD data, 94 died, and 323 were hospitalized. 6MWD fell by 29.7 m (SD, 82.9 m) more among those who died than among survivors (P < 0.001). A reduction in distance of more than 30 m conferred a hazard ratio of 1.93 (95% confidence interval, 1.29-2.90; P = 0.001) for death. No significant difference was observed for first hospitalization. Weak relationships only were observed with change in lung function or health status.


CONCLUSIONS
A reduction in the 6MWD of 30 m or more is associated with increased risk of death but not hospitalization due to exacerbation in patients with chronic obstructive pulmonary disease and represents a clinically significant minimally important difference.