Evaluation of spondyloarthritis-specific health utility based on ASAS health index (U-ASAS-HI) among the disease subtypes

\(\bf Objectives\) To compare the spondyloarthritis (SpA) specific universal health utility estimation from the ASAS health index (U-ASAS-HI) with the generic EuroQol-5D-3L (EQ-5D-3L) utility among SpA subtypes and to understand the contribution of health-, personal- and country-level factors to the U-ASAS-HI. \(\bf Methods\) Ancillary analysis of the ASAS-PERipheral involvement in SpondyloArthritis (PerSpA) study including patients who completed both ASAS-HI and EQ-5D-3L. Correlations between U-ASAS-HI and EQ-5D-3L were tested overall and by subtype (axial SpA, peripheral SpA and psoriatic arthritis (PsA)). Health and contextual determinants of U-ASAS-HI were evaluated using multivariable linear mixed-effects models with country as level. \(\bf Results\) 4158 patients were included, mean age 44 (SD:13) and 61% male. Mean U-ASAS-HI was 0.44 (SD:0.30) and mean EQ-5D-3L was 0.71 (SD:0.21), with numerically minor differences between subtypes. Correlations between U-ASAS-HI and EQ-5D-3L were consistently strong between subgroups (range 0.74–0.76). Linear mixed-effects modelling showed health outcomes, including disease activity (axial spondyloarthritis disease activity score; \(\beta\)=−0.030, 95% CI −0.038 to −0.021), physical function (bath ankylosing spondylitis functional index; \(\beta\)=−0.044, 95% CI −0.048 to −0.041), anxiety/depression (EQ-5D-3L q5; \(\beta\)=−0.147, 95% CI −0.160 to −0.134) and fibromyalgia (fibromyalgia rapid screening tool; \(\beta\)=−0.068, 95% CI −0.083 to −0.053) were strong predictors of lower U-ASAS-HI. Additionally, female gender, PsA subtype, axial involvement, fatigue and having no employment were associated with lower U-ASAS-HI while older age and university education were associated with higher U-ASAS-HI. The random-effects model indicated an intraclass correlation coefficient of 6% in total variance attributable to differences between countries. \(\bf Conclusion\) The universal U-ASAS-HI captures the broad range of aspects relevant to valuing SpA health states across SpA subtypes. The lower absolute values of U-ASAS-HI reflect the wider disutility associated with SpA.