The following is a summary of “Clinimetric Validation of the Assessment of Spondyloarthritis International Society Health Index in Patients With Radiographic Axial Spondyloarthritis in Ixekizumab Trials,” published in the June 2023 issue of Rheumatology by Kiltz et al.

The purpose of this study is to evaluate the test-retest reliability, construct validity, known group discrimination, and responsiveness of the Assessment of the SpondyloArthritis International Society Health Index (ASAS HI) for assessing functioning, disability, and health in patients with radiographic axial spondyloarthritis (r-axSpA). About 2 randomized, placebo-controlled, active-controlled phase III ixekizumab studies (COAST-V, N = 341; COAST-W, N = 316) generated data. 

Test-retest reliability (i.e., intraclass correlation coefficients [ICCs] between ASAS HI scores at screening and baseline), construct validity (i.e., Spearman correlation with standard r-axSpA outcome measures), known groups discrimination (i.e., 1-way ANOVA comparing the ASAS HI with different disease activity categories, as measured by the Ankylosing Spondylitis Disease Activity Score [ASDAS]), and responsiveness (i.e., Spearman correlation between changes in the ASAS HI and changes in the Bath Ankylosing Spondylitis Functional Index [BASFI], the Bath Ankylosing Spondylitis Disease Activity Index [BASDAI], the ASDAS, and the Patient Global Assessment [PtGA] as well as ANOVA comparing changes in the ASAS HI with various responder categories). The test-retest reliability coefficients for COAST-V and COAST-W were 0.78 and 0.76, respectively, indicating good agreement. 

Between the ASAS HI and the BASDAI, moderate to substantial correlations (r = 0.40-0.61) were found. At baseline and week 16, there were statistically significant differences (all P<0.001) between the mean ASAS HI scores for subgroups based on ASDAS-defined disease activity categories. Changes in the ASAS HI correlated moderately to firmly with the BASFI, BASDAI, ASDAS, and PtGA from baseline to week 16. The ASAS HI is statistically distinguished between ASAS, BASDAI, and ASDAS response groups (P<0.001). In 2 clinical investigations, the ASAS HI demonstrated reliability, construct validity, discrimination between known groups, and responsiveness in adults with r-axSpA.

Source: jrheum.org/content/50/6/754