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.