Validity and reliability of EQ-5D-5L among patients with axial spondyloarthritis in Singapore.

Objective: This study aims to evaluate the reliability and validity of EuroQOL-5 Dimensions-5 Levels (EQ-5D-5L) among patients with axial spondyloarthritis (SpA) in Singapore.

Methods: A cross-sectional study was conducted involving patients with axial SpA in an Asian tertiary hospital from 2017 to 2018. This study followed the COnsensus-based Standards for selection of health Measurement Instruments framework. Construct validity was evaluated by testing 22 a priori hypotheses with other patient-reported outcomes measures. Cronbach's alpha was used to estimate the internal consistency of the EQ-5D-5L, while its test-retest reliability was assessed using weighted kappa and the intraclass correlation coefficient (ICC). The measurement error was assessed by analyzing minimal detectable change (MDC).

Results: The median age of included patients (n=118) was 35 years (interquartile range: 28, 49). Ninety-six (81.4%) patients were male, while 112 (94.9%) patients were of Chinese ethnicity. The EQ-5D-5L demonstrated good internal consistency with a Cronbach's alpha of 0.79. The test-retest reliability of the EQ-5D-5L was good with a weighted kappa of ≥0.61 for mobility, self-care, usual activities, and anxiety/depression; the ICC was 0.92 and 0.99 for the EQ-5D-5L index and visual analog scale (VAS) scores, respectively. The weighted kappa for the EQ-5D-5L pain/discomfort was moderate [0.53, 95% confidence interval: 0.41-0.60]. The MDC for EQ-5D-5L index and VAS scores was 0.06 and 4.5, respectively. Convergent validity was supported as all hypotheses were confirmed in the results.

Conclusion: This study supports EQ-5D-5L as a valid and reliable instrument for assessing health-related quality of life among patients with axial SpA in Singapore.