Evaluating the correspondence between the EQ-5D-5L and disease severity and quality of life in adults and adolescents with cystic fibrosis

Background: The EQ-5D is the recommended measure to capture health-related quality of life (HRQoL), recognised for use in health technology appraisal bodies. In order to assess whether it is appropriate to use the EQ-5D for making decisions about the cost-utility of treatments in cystic fibrosis (CF), this study assesses the performance of the EQ-5D-5L in adults and adolescents with CF.  
Method: This was a cross-sectional observational survey study of patients with CF attending a single large CF centre. Participants were asked to complete a survey that included two HRQoL measures; the EQ-5D-5L and CF Quality of Life (CFQoL) questionnaires.  
Results: Among 213 participants, the median EQ-5D-5L index score was 0.76 (IQR 0.66 – 0.84) and the visual analogue (EQ-VAS) was 70 (60 – 80). Both the EQ-5D index and EQ-VAS discriminated between disease severity based on lung function (p=0.01 and p<0.01, respectively) and pulmonary exacerbation (p=0.02 and p<0.01, respectively); however, EQ-VAS differentiated between more lung function severity groups compared to EQ-5D index. The EQ-5D-5L demonstrated convergent validity as its dimensions, index score, and EQ-VAS had significant correlations with most CFQoL domains. Though, EQ-VAS significantly predicted more domains of CFQoL (4 domains) compared to EQ-5D index (only 1 domain).  
Conclusion: The generic EQ-5D-5L performed adequately in discriminating between CF disease severity, and its index score and EQ-VAS had moderate correlations with CFQoL. However, using a complementary condition-specific measure alongside the EQ-5D-5L can provide better insight of HRQoL in CF and benefit the process of cost-utility analysis.