A recent nationwide observational study published in Rheumatic and Musculoskeletal Diseases Open found that higher baseline C-reactive protein (CRP) levels were associated with greater 12-month treatment retention among patients with axial spondyloarthritis (axSpA) initiating their first tumour necrosis factor inhibitor (TNFi). However, no similar association was observed among patients starting their first interleukin-17 inhibitor (IL-17i).
The study analysed data from the DANBIO registry and included 3,387 patients with axSpA who initiated their first IL-17i (n=601) or first TNFi (n=2,786) between 2015 and 2024. Baseline CRP levels were categorised as low (<5 mg/L), intermediate (5–10 mg/L), or high (>10 mg/L). Among IL-17i initiators, 57% had low, 17% intermediate and 26% high CRP levels, compared with 48%, 20% and 32%, respectively, among TNFi initiators. The treatment groups also differed substantially in previous biologic exposure, with 95% of IL-17i initiators being biologic-experienced, compared with 99% of TNFi initiators being biologic-naïve.
At 12 months, treatment retention among IL-17i recipients was 51%, 53% and 55% in the low-, intermediate- and high-CRP groups, respectively. Corresponding retention rates among TNFi recipients were 63%, 66% and 72%. Cox regression analysis, using low CRP as the reference category, showed no clear association between baseline CRP and treatment discontinuation among IL-17i recipients. The hazard ratios (HRs) for discontinuation were 0.96 (95% confidence interval [CI] 0.68–1.19) for intermediate CRP and 0.90 (95% CI 0.68–1.19) for high CRP.
In contrast, higher baseline CRP levels were associated with a lower risk of treatment discontinuation among TNFi recipients. The HR for discontinuation was 0.86 (95% CI 0.73–1.02) for intermediate CRP and 0.72 (95% CI 0.62–0.84) for high CRP compared with low CRP. The findings remained consistent across subgroups based on sex and radiographic status.
Higher baseline CRP levels were also associated with greater remission rates with both treatment classes. Among IL-17i recipients, remission rates were 6%, 8% and 11% across the low-, intermediate- and high-CRP groups, respectively. Among TNFi recipients, corresponding remission rates were 19%, 22% and 32%.
The findings indicate that, in routine clinical practice, IL-17i therapy was predominantly used in biologic-experienced patients, whereas TNFi therapy was primarily initiated in biologic-naïve patients with axSpA. Higher baseline CRP levels were associated with greater treatment retention among patients receiving their first TNFi but not among those receiving their first IL-17i. Higher CRP levels were also associated with higher remission rates with both drug classes.
The authors noted that CRP levels at treatment initiation may help clinicians anticipate treatment outcomes in routine practice. However, the findings do not establish superiority of either treatment class, as the study was observational and did not involve a head-to-head comparison between TNFi and IL-17i therapies.
Reference
Høegh Pedersen A, Jensen KY, Hetland ML, Glintborg B. 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 Jun 16;12(2):e006807.