Responsiveness and minimal clinically important difference of SGRQ-I and K-BILD in idiopathic pulmonary fibrosis

Abstract

Background: Idiopathic pulmonary fibrosis (IPF) specific version of St. George's Respiratory Questionnaire (SGRQ-I) and King's Brief Interstitial Lung Disease questionnaire (K-BILD) are validated health-related quality of life (HRQL) instruments, but no or limited data exist on their responsiveness and minimal clinically important difference (MCID). The objectives of this study were to assess responsiveness of SGRQ-I and K-BILD and determine MCID separately for deterioration and improvement in a large, prospective cohort of patients with IPF in a real-world setting.

Methods: Consecutive patients with IPF were recruited. SGRQ-I, K-BILD, SGRQ, Shortness of Breath Questionnaire, pulmonary function tests and 6-min walk test measurements were obtained at baseline and at six and 12 months; at six and 12 months, patients also completed Global Rating of Change Scales. Responsiveness was assessed using correlation coefficients and linear regression. Cox regression was used for mortality analyses. MCID was estimated using receiver operating characteristic curves with separate analyses for improvement and deterioration.

Results: A total of 150 IPF patients were included and 124 completed the 12-month follow-up. Based on all HRQL anchors and most physiological anchors, responsiveness analyses supported the evidence pointing towards SGRQ-I and K-BILD as responsive instruments. Multivariate analyses showed an association between SGRQ-I and mortality (HR: 1.18, 95% CI: 1.02 to 1.36, p = 0.03) and a trend was found for K-BILD (HR: 0.82, 95% CI: 0.64 to 1.05, p = 0.12). MCID was estimated for all domains of SGRQ-I and K-BILD. MCID for improvement differed from deterioration for both SGRQ-I Total (3.9 and 4.9) and K-BILD Total (4.7 and 2.7).

Conclusions: SGRQ-I and K-BILD were responsive to change concerning both HRQL and most physiological anchors. MCID was determined separately for improvement and deterioration, resulting in different estimates; especially a smaller estimate for deterioration compared to improvement in K-BILD.

Trial registration: Clinicaltrials.gov, no. NCT02818712. Registered 30 June 2016.

Keywords: Health-related quality of life; IPF; IPF-specific version of St. Georges respiratory questionnaire; Idiopathic pulmonary fibrosis; K-BILD; King’s Brief Interstitial Lung Disease questionnaire; Longitudinal validity; Responsiveness; SGRQ-I; minimal clinically important difference.

Conflict of interest statement

OH, EB and TSP have received an unrestricted grant from Boehringer Ingelheim for the current work. Outside the current work, TSP, JRD and EB have received fees from Roche and Boehringer Ingelheim. SBS and NH declare no competing interests.

Figures

Fig. 1

SGRQ-I (A) and K-BILD (B) Total score at baseline, six months and 12 months. Dots indicate mean scores and whiskers illustrate 95% confidence intervals. SGRQ-I: IPF-specific version of the Saint George’s Respiratory Questionnaire, K-BILD: King’s Brief Interstitial Lung Disease questionnaire

Fig. 2

Results of linear regression comparing SGRQ-I (A) and K-BILD (B) scores from baseline to 12 months in groups of different stages of disease. Patients were divided into three equally large groups according to stage of disease by SOBQ, SGRQ, FVC, DLCO and 6MWD. For GRCS, patients were divided into deteriorated, unchanged or improved (see Additional file 1 for group details). *: p < 0.05 for linear effect. Δ: Change from baseline to 12 months; SGRQ-I: IPF-specific version of the Saint George’s Respiratory Questionnaire, K-BILD: King’s Brief Interstitial Lung Disease questionnaire, CI: Confidence interval, GRCS: Global Rating of Change Scales, SOBQ: University of California San Diego Shortness of Breath questionnaire, SGRQ: Saint George’s Respiratory Questionnaire, FVC: Forced vital capacity, DLCO: Diffusing capacity of the lung for carbon monoxide, 6MWD: Distance walked during the 6-min walk test