COMPARATIVE EVALUATION OF SERUM NEOPTERIN AND BIOPYRRIN IN AXIAL SPONDYLOARTHRITIS: A CROSS-SECTIONAL STUDY

Abstract

Objective: To compare serum neopterin and biopyrrin levels in axial spondyloarthritis (axSpA) and healthy controls, and to assess their associations with clinical phenotypes and diagnostic performance.

Methodology: This multicenter cross-sectional study included 119 patients with axSpA and 130 healthy controls. Serum neopterin and biopyrrin levels were measured and compared across treatment exposure, C-reactive protein (CRP) status, and radiographic classification. Diagnostic performance was evaluated using receiver operating characteristic (ROC) analysis. Multivariable linear regression was used to assess independent associations after adjustment for age, sex, and body mass index.

Results: Both biomarkers were significantly higher in axSpA compared with controls. Neopterin showed moderate discrimination (AUC 0.74; 95% CI 0.68–0.80; p<0.001), while biopyrrin showed weaker performance (AUC 0.60; 95% CI 0.53–0.67; p=0.018). Biomarker levels were highest in treatment-naïve patients and remained elevated in CRP-normal disease. Neopterin levels were higher in non-radiographic axSpA. In multivariable analysis, neopterin remained independently associated with axSpA, whereas biopyrrin did not.

Conclusion: Neopterin and biopyrrin are elevated in axial spondyloarthritis, with neopterin demonstrating independent association with disease status and moderate diagnostic performance. Persistent elevation in CRP-normal disease suggests ongoing immuno-oxidative activity beyond conventional inflammatory measures. These findings support neopterin as a promising complementary biomarker for disease characterization, warranting further longitudinal validation.