Psychometric properties of patient reported outcome measures in idiopathic pulmonary fibrosis.

BACKGROUND Various patient reported outcome measures (PROMs) are used in idiopathic pulmonary fibrosis (IPF). We aimed to describe their psychometric properties, assess their relationship with 1-year mortality and determine their minimal clinically important differences (MCIDs). METHODS In a prospective multicentre study, participants with IPF completed the King's Brief Interstitial Lung Disease Questionnaire (K-BILD), the modified Medical Research Council (mMRC) dyspnoea scale, St George's Respiratory Questionnaire (SGRQ) and University of California, San Diego shortness of breath questionnaire (UCSD-SOBQ) three-monthly intervals over a 12-month period. Forced vital capacity (FVC) was matched with questionnaires and mortality was captured. Anchor- and distribution-based methods were used to derive MCID. RESULTS Data were available from 238 participants. All PROMs had good internal consistency and high degree of correlations with other tools (except UCSD-SOBQ correlated poorly with FVC). There were significant associations with mortality for K-BILD (hazard ratio 16.67; 95% CI 2.38-100) and SGRQ (hazard ratio 4.65; 95% CI 1.32-16.62) but not with the other PROMs or FVC. The median MCID (range) for K-BILD was 6.3 (4.1-7.0), SGRQ was 7.0 (3.8-9.6), mMRC was 0.4 (0.1-0.5) and UCSD-SOBQ was 9.6 (4.1-14.2). CONCLUSIONS The K-BILD was related to other severity measures and had the strongest relationship with mortality.