Psychometric properties of the St George’s Respiratory Questionnaire in patients with idiopathic pulmonary fibrosis: insights from the INPULSIS trials

INTRODUCTION: We evaluated the psychometric properties of the St George’s Respiratory Questionnaire (SGRQ) in patients with idiopathic pulmonary fibrosis (IPF) using data from the two INPULSIS trials. METHODS: Data from 1061 patients treated with nintedanib or placebo were pooled. Internal consistency, test–retest reliability, construct validity, known-groups validity, responsiveness and responder thresholds were examined. RESULTS: Cronbach’s α was 0.93 for SGRQ total score and >0.75 for domain scores. In patients with stable disease based on change in forced vital capacity (FVC) ≤5% predicted or ‘no change’ on Patient’s Global Impression of Change, intraclass correlation coefficients for the SGRQ total score were 0.72 or 0.76, respectively. Moderate to strong correlations were observed between SGRQ total and domain scores and the Cough and Sputum Assessment Questionnaire cough domains (−0.34 to −0.65), University of California San Diego Shortness of Breath Questionnaire (0.56 to 0.83) and EuroQol 5-Dimensional Quality of Life Questionnaire Visual Analogue Scale (−0.41 to −0.55); correlations with FVC % predicted were weak (−0.24 to −0.30). Longitudinal correlations between changes in SGRQ total score and these patient-reported outcomes over 52 weeks were moderate. Changes in SGRQ total, impact and activity scores were sensitive to detecting improvement or deterioration in FVC >10% predicted at week 52. Collectively, distribution-based and anchor-based approaches suggested using a change of 4–5 points in SGRQ total score as a starting point for responder analyses. CONCLUSIONS: The psychometric properties of the SGRQ support its use as a measure of health-related quality of life in patients with IPF.