A ROUTINE blood marker may predict how well biologic drugs work in axial spondyloarthritis, a Danish nationwide study finds, with higher inflammation predicting better outcomes for one drug class but not the other.
Inflammation Markers and Biologic Choice in Axial Spondyloarthritis
C-reactive protein (CRP), a marker of inflammation, has long been tied to better responses to tumour necrosis factor inhibitors (TNFi) in axial spondyloarthritis, while interleukin-17 inhibitors (IL-17i) seemed effective regardless. Real-world evidence for IL-17i was lacking, prompting this study to test how baseline CRP shaped outcomes for both drug classes.
Study Design and CRP Stratification
The nationwide observational study drew on Denmark’s DANBIO registry, including patients with axial spondyloarthritis who began their first IL-17i or first TNFi between 2015 and 2024. Outcomes were 12-month treatment retention and Bath Ankylosing Spondylitis Disease Activity Index remission, stratified by baseline CRP as low (below 5), intermediate (5 to 10), or high (above 10 mg/L). Kaplan-Meier plots and Cox regression assessed retention and discontinuation for each drug separately, with substratification by sex and radiographic status. Of 3,387 patients, 601 received IL-17i (95% TNFi-experienced) and 2,786 received TNFi (99% biologic-naive).
Diverging Effects of CRP by Drug Class
For IL-17i, 12-month retention was similar across CRP strata at 51%, 53%, and 55% (low, intermediate, high), with Cox models showing no clear association (intermediate CRP: HR 0.96, 95% CI 0.68 to 1.19; high CRP: HR 0.90, 95% CI 0.68 to 1.19). For TNFi, retention rose with CRP at 63%, 66%, and 72%, and higher CRP was linked to lower discontinuation risk (intermediate: HR 0.86, 95% CI 0.73 to 1.02; high: HR 0.72, 95% CI 0.62 to 0.84). Remission rates rose with CRP for both, from 6% to 11% for IL-17i and 19% to 32% for TNFi.
Informing Treatment Expectations
The authors concluded that baseline CRP predicted retention for a first TNFi but not a first IL-17i, with patterns holding across sex and radiographic status. Higher CRP tracked with greater remission for both classes. Because up to half of patients with axial spondyloarthritis present with normal CRP, they suggested the marker could help set realistic outcome expectations when starting treatment, though the differing prescription patterns mean the classes cannot be directly compared here.
Reference
Høegh Pedersen A et al. Impact of C reactive protein on effectiveness of interleukin-17 and tumour necrosis factor inhibitors in axial spondyloarthritis: a Danish nationwide observational study. RMD Open. 2026;12:e006807.
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