Six-minute-walk distance predicts waiting list survival in idiopathic pulmonary fibrosis

Abstract

Rationale: Functional studies may be useful to predict survival in idiopathic pulmonary fibrosis (IPF). Various cutoffs of 6-min-walk distance (6MWD) have been suggested to identify patients at a high risk of death.

Objectives: To examine the association between 6MWD and survival in patients with IPF listed for lung transplantation, and to identify sensitive and specific cutoffs for predicting death at 6 mo.

Methods: We performed a retrospective cohort study of 454 patients classified as having IPF listed for lung transplantation with the United Network for Organ Sharing between June 30, 2004 and July 22, 2005.

Measurements and main results: Lower 6MWD was associated with an increased mortality rate (p value for linear trend < 0.0001). Patients with a walk distance less than 207 m had a more than fourfold greater mortality rate than those with a walk distance of 207 m or more, despite adjustment for demographics, anthropomorphics, FVC % predicted, pulmonary hypertension, and medical comorbidities (adjusted rate ratio, 4.7; 95% confidence interval, 2.5-8.9; p < 0.0001). 6MWD was a significantly better predictor of 6-mo mortality than was FVC % predicted (c-statistic = 0.73 vs. 0.59, respectively; p = 0.02).

Conclusions: Lower 6MWD was strongly and independently associated with an increased mortality rate for wait-listed patients classified as having IPF. 6MWD was a better predictor of death at 6 mo than was FVC % predicted.

Figure 1.

Receiver operating characteristic (ROC) curves of 6-min-walk distance (6MWD; solid line) and FVC % predicted (dashed line) for 6-mo mortality. The areas under the ROC curves (95% confidence intervals) are 0.73 (0.66–0.81) for 6MWD and 0.59 (0.49–0.69) for FVC % predicted (p = 0.02 for the comparison between curves). Numerals inside the figure denote the 6MWD (in meters) at selected points along the ROC curve.

Figure 2.

Kaplan-Meier survival estimates for patients with idiopathic pulmonary fibrosis listed for lung transplantation. Solid line, 6MWD ⩾ 207 m; dotted line, 6MWD < 207 m.