Responsiveness of spondyloarthritis-specific health utilities based on the ASAS Health Index (U-ASAS-HI): an ancillary analysis from the ASAS-HI validation study

Objectives To assess responsiveness of the spondyloarthritis (SpA)-specific universal health utility from the ASAS Health Index (U-ASAS-HI) compared with generic health utilities (EQ-5D-5L and SF-6D).Methods Data were used from patients with SpA participating in the ASAS-HI international validation study and starting TNF inhibitor (TNFi), conventional synthetic DMARD (csDMARD) or NSAID. A priori hypotheses on correlation of change in utility and change in external health anchors between baseline and follow-up were tested. Standardized response mean (SRM) and Cohen's effect size (ES) were calculated in each treatment group. The ability of changes in utilities to discriminate between BASDAI-50% (non)-responders was assessed by standardized estimate of change and receiver operating characteristic (ROC) analyses.Results 219 patients were included (110 TNFi, 37 csDMARD, and 72 NSAID). Mean (s.d.) age was 37 (13) years and 63% were male. Hypotheses on correlations of change scores were confirmed for 75% of comparisons for U-ASAS-HI and EQ-5D-5L, but not for SF-6D. As expected, SRM and ES for the U-ASAS-HI were large in the TNFi-treated group, moderate in the csDMARD group and small to moderate in the NSAID group. The hypothesized larger SRM and ES for U-ASAS-HI compared with EQ-5D and SF-6D could not be consistently confirmed across the three treatment groups. Ability to discriminate between BASDAI-50% responders and non-responders did not differ among utility instruments in ROC comparison.Conclusion In a context where change is expected, the SpA-specific U-ASAS-HI correlates as expected with changes in other SpA-specific outcomes and shows good responsiveness, which is similar to but not better than for generic utilities.