Change in 6-minute walk test can predict prognosis in idiopathic pulmonary fibrosis

Abstract

Background: Six-minute walk test (6MWT) is commonly performed in patients with idiopathic pulmonary fibrosis (IPF). We investigated whether a change in 6MWT during 1 year are associated with a worse outcome. Aim: To assess the 1-year change in 6-minute walk distance (6MWD) and lowest room air oxygen saturation during 6MWT (L-SpO2) and its impact on disease prognosis. Methods: Ninety-two patients, all on anti-fibrotic treatment, from the Swedish IPF registry were included. All patients had a baseline and a 1-year follow-up 6MWT. The proportions of patients with a decline in 6MWD and L-SpO2 ≥ 5% and ≥ 10% respectively were calculated. Its ability to predict 2-year transplant-free survival was estimated, adjusted for baseline age, gender, body mass index (BMI), forced vital capacity (FVC) % of predicted and diffusion capacity for carbon monoxide (DLCO) % of predicted. Results: L-SpO2 were lower after 1 year compared to baseline (84.7% vs.86.4%; p=0.002), but there was no difference in 6MWD (448m vs. 454m; p=0.407). Patients with ≥5% decline in 6MWD after 1 year, had less survival compared to those without (38.4months vs. 46.2 months, p=0.002). Patients with ≥10% decline in L-SpO2 had a survival of 23.8 months compared with 44.3 months for those without (p=0.005). A decline in 6MWD of ≥5% predicted survival at 2 years (p=0.019), after adjusted baseline age, gender, BMI, FVC and DLCO. Conclusions: One-year change in 6MWT can help to identify the outcome in IPF in patients on anti-fibrotic treatment. Both walking distance and L-SpO2 were associated to poorer transplant-free survival. Our findings support the use of 6MWT as a clinically relevant test in the follow-up of patients with IPF.