Validation of the IPF-specific version of St. George’s Respiratory Questionnaire in Danish

Abstract

Introduction: Quality of life is impaired in patients with idiopathic pulmonary fibrosis (IPF) due to both physical and psychological deficits. The IPF-specific version of St. George’s Respiratory Questionnaire (SGRQ-I) is a validated measure of health-related quality of life. This study was conducted to validate the Danish version of SGRQ-I.

Methods: At baseline, patients with IPF completed SGRQ-I, St. Georges Respiratory Questionnaire (SGRQ), University of California, San Diego Shortness of Breath Questionnaire (SOBQ) and Short Form-36 (SF-36), and lung function tests were performed. SGRQ-I and Global Rating of Change Scales were completed 14 days later. Internal consistency, concurrent validity, test-retest reliability and known groups validity were estimated.

Results: The questionnaires were completed by 150 patients at baseline and by 144 patients after 14 days. Internal consistency was high in SGRQ-I (Cronbach’s α: 0.92). Good concurrent validity of SGRQ-I compared to SGRQ was demonstrated by high intraclass correlation coefficient (ICC 0.97) and Bland Altman plots. Also, SGRQ-I had moderate to strong correlations to SOBQ and SF-36 (r = 0.46-0.80) along with moderate to weak correlations to lung function and 6-minute walk test (r = 0.30-0.50). High ICC (0.92) and a Bland Altman plot indicated good test-retest reliability of the questionnaire. SGRQ-I was able to discriminate patients with different stages of disease.

Conclusion: The Danish version of the SGRQ-I is valid and reliable as a measure of quality of life in patients with IPF and performs equally to the English version. Studies of responsiveness of SGRQ-I and factors associated with impaired quality of life are ongoing.