Validation of the SGRQ-I derived from SGRQ

Abstract

Introduction: Patients (pts) with idiopathic pulmonary fibrosis (IPF) have impaired health-related quality of life (HRQL). The St. George’s Respiratory Questionnaire (SGRQ) is also available in an IPF specific version (SGRQ-I). The aim of this study was to transform SGRQ into a derived version of SGRQ-I (SGRQ-I_der), to examine the validity of SGRQ-I_der and to compare SGRQ-I_der to the original SGRQ-I.

Methods: SGRQ results were transformed into SGRQ-I_der in a cohort used to validate SGRQ-I. At baseline (BL) and 12 months, pts completed SGRQ, SGRQ-I, K-BILD, UCSD Shortness of Breath questionnaire, SF-36, and pulmonary function tests (PFT). Both cross-sectional and longitudinal validation were performed.

Results: Questionnaires were completed by 150 pts at BL and 124 pts at 12 months. At BL, internal consistency was high in SGRQ-I_der (Cronbach’s α: 0.92). Good concurrent validity of SGRQ-I_der compared to SGRQ-I was demonstrated by a high intraclass correlation coefficient (ICC 2,1: 0.99), Bland Altman plot, moderate to strong correlations with other HRQL instruments (r=0.46–0.80) and weaker correlations with PFT (r=0.29–0.51). A high ICC (0.91) and a Bland Altman plot indicated good test-retest reliability. SGRQ-I_der was able to discriminate pts with different stages of disease based on PFT, oxygen therapy and GAP index. Responsiveness was demonstrated by moderate to strong correlations of change from BL in SGRQ-I_der with other HRQL instruments (r=0.55–0.95) and weaker correlations with PFT (r=0.24–0.48). Minimal clinically important difference after 12 months for improvement was 3.5 and 5.7 for deterioration.

Conclusion: The SGRQ-I_der is valid both cross-sectionally and longitudinally and performs comparably to SGRQ-I. This was a collaborative study.