Six-minute walking test outweighs other predictors of mortality in idiopathic pulmonary fibrosis. A real-life study from the Swedish IPF registry

Abstract Background and objective Idiopathic pulmonary fibrosis (IPF) is a disease characterized by a progressive loss of lung function, a restrictive ventilatory impairment, and a high five-year mortality. Our aim was to characterize clinical features of IPF at baseline and to assess which of those that would predict mortality. Methods We used baseline data at inclusion collected from the Swedish IPF registry between January 2014 and October 2018. Patients were followed for at least six months. Demographics, lung function (forced vital capacity (FVC), total lung capacity (TLC), diffusion capacity of carbon monoxide (DLCO%)), 6-min walking test (6MWT), lowest oxygen saturation during 6MWT (L-SpO2), King's brief interstitial lung disease health status questionnaire (K-BILD) scores were collected. GAP index and Charlson Comorbidity Index (CCI) were calculated. Transplant-free survival was registered during the follow-up time. Results Two hundred and twenty patients were included in the study. Fifty-seven (26%) died and six (3%) underwent lung transplant during a mean follow-up time of 24 months. Out of 220 patients, 63 patients (29%) had a FVC% equal or over 80% of predicted at baseline. Only 17 out of 155 (11%) patients had a normal TLC%. Walking distance during a 6MWT was an independent predictor of outcome death/transplant (HR 0.80, 95%CI 0.65–0.99, p = 0.037), when adjusted for TLC%, K-BILD and GAP stage in a multivariate cox regression model. Conclusion Our results confirm the relevance of the 6MWT as main predictor of mortality at diagnosis in IPF patients.