Validation of the King’s Brief Interstitial Lung Disease questionnaire in Idiopathic Pulmonary Fibrosis

Abstract

Abstract Background Health-related quality of life (HRQL) is impaired in patients with idiopathic pulmonary fibrosis (IPF). The King’s Brief Interstitial Lung Disease questionnaire (K-BILD) is a validated measure of HRQL, but no previous studies have focused on the validity of K-BILD in IPF. Moreover, the relationship between K-BILD and dyspnoea or the 6-min walk test (6MWT) has not been assessed. The aim of this study was to validate K-BILD in the largest cohort of patients with IPF to date and assess how K-BILD correlates to dyspnoea and 6MWT. Methods Firstly, K-BILD was translated into Danish using validated translation procedures. Consecutive patients with IPF were recruited. At baseline, patients completed K-BILD, the IPF-specific version of St. Georges Respiratory Questionnaire, University of California, San Diego Shortness of Breath Questionnaire (SOBQ) Short Form-36, and pulmonary function tests and 6MWT were performed. After 14 days, K-BILD and Global Rating of Change Scales were completed. Internal consistency, concurrent validity, test-retest reliability and known groups validity were assessed. Analyses were also performed in subgroups of patients with different time since diagnosis. Results At baseline, 150 patients with IPF completed the questionnaires, and 139 patients completed the questionnaires after 14 days. K-BILD had a high internal consistency (Cronbach’s α = 0.92). The concurrent validity was strong compared to SOBQ (r = − 0.66) and moderate compared to 6MWT (r = 0.43). Intraclass correlation coefficients (ICC = 0.91) and a Bland Altman plot demonstrated a good reliability. K-BILD was also able to discriminate between patients with different stages of disease (p < 0.002, Δscore > 7.4) and most results were comparable in patients with different time since diagnosis. Conclusion K-BILD is a valid and reliable instrument in patients with IPF and in patients with different time since diagnosis. To a major extent, K-BILD scores reflected the impact of dyspnoea on HRQL and the impact of physical functional capacity measured by the 6MWT to a moderate degree. Compared to PFTs alone, K-BILD provides additional information on the burden of living with IPF, and importantly, K-BILD is simple to implement in both research and clinical contexts. Trial registration Clinicaltrials.org (NCT02818712) on 30 June 2016.