Discriminating capacity of the ASAS health index in patients with axial spondyloarthritis treated with ixekizumab.

Objective: To test the discriminating capacity of different thresholds of the Assessment of SpondyloArthritis international Society Health Index (ASAS HI) in placebo-controlled trials of patients with axial spondyloarthritis (axSpA), including radiographic (r-axSpA) and non-radiographic (nr-axSpA) subtypes.

Methods: The discriminating capacities of absolute (≥2.0-≥4.0 points) and relative (≥20%-≥50%) ASAS HI improvement thresholds were evaluated in patients with axSpA from three COAST trials (COAST-V, COAST-W, and COAST-X) of ixekizumab every 4 weeks (IXE Q4W) vs. placebo. Threshold-based response rates at Week 16 were compared between trial arms using Fisher's exact test. Odds ratios and phi coefficients were used to evaluate how strongly each improvement threshold was associated with treatment allocation in a given trial. Missing data were handled using non-responder imputation.

Results: ASAS HI data were available at baseline and Week 16 for 587 patients in IXE Q4W and placebo arms. The ASAS HI ≥30% improvement threshold effectively discriminated treatment allocation in all trials; significant differences were observed between IXE Q4W and placebo in r-axSpA (COAST-V: p = 0.026; COAST-W: p = 0.023) and nr-axSpA (COAST-X: p = 0.040). Lower absolute (≥2.0-≥3.0 points) and relative (≥20%-≥30%) thresholds discriminated effectively in COAST-W, whereas higher absolute (≥3.5-≥4.0 points) and relative (≥30%-≥50%) thresholds discriminated effectively in COAST-V. In COAST-X, ≥30%, ≥40%, and ≥50% thresholds discriminated effectively. Phi coefficients were small (<0.3) across all trials and thresholds.

Conclusions: Several ASAS HI improvement thresholds discriminated axSpA patients in treatment vs. placebo arms at Week 16. The ASAS HI ≥30% improvement threshold discriminated across all three COAST trials.