Performance of spondyloarthritis-specific health utilities based on ASAS Health Index: an ancillary analysis from ASAS-HI validation study

OBJECTIVES: To compare the utility values of Spondyloarthritis (SpA)-specific ASAS Health Index (U-ASAS-HI) to generic utilities and to understand the contribution of health outcomes, personal- and country-level factors to the U-ASAS-HI. METHODS: Ancillary analysis of the ASAS-HI international validation study. SpA patients who completed the ASAS-HI, 5-level EuroQol-5D (EQ-5D-5L) and Short Form-36 (SF-36) questionnaires were selected, and utilities calculated. Correlations between U-ASAS-HI and generic utility values were tested. Potential explanatory variables were evaluated in a linear multivariable mixed-effects model analysis with multilevel modeling fitted by country. RESULTS: 1425 patients were included, with a mean age of 42 (Standard Deviation, SD : 13.5) and 65% male. The mean utility scores were EQ-5D-5L 0.75 (SD : 0.11), SF-6D 0.72 (SD : 0.24), and U-ASAS-HI 0.42 (SD : 0.29). Correlation between U-ASAS-HI and EQ-5D-5L and SF-6D was strong (r = 0.75 and r = 0.72; p< 0.001, respectively). The linear mixed-effects model showed that worse disease activity (ASDAS) and lower physical function (BASFI) were associated with lower U-ASAS-HI. Additionally, younger age, female gender, higher comorbidity score, and symptoms of depression were associated with lower U-ASAS-HI. SpA subtype had no influence on health utility. The random effects model indicated an intercept SD : 0.045 with a 5.5% variance ratio between countries and the total U-ASAS-HI variation. CONCLUSION: The U-ASAS-HI captures the physical and mental impact of SpA, as well as personal contextual factors such as age, gender, and comorbidities. The influence of the country of residence seems negligible. The U-ASAS-HI algorithm has sufficient support to be used in health economic evaluations for SpA patients across different countries.