Tailoring Inflammatory Biomarker Assessment in Axial Spondyloarthritis: A Comparative Study of Erythrocyte Sedimentation Rate and C-Reactive Protein Across Disease Profiles

Background: Personalized medicine in axial spondyloarthritis (axSpA) requires accurate tools to assess inflammation and tailor disease monitoring. The role of traditional biomarkers such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) remains controversial due to limited sensitivity and variability across disease profiles. Objective: To compare the performance of ESR and CRP in different clinical scenarios of axSpA, including disease activity, functional impact, severity, disease duration, and exposure to biologic therapy. Methods: We conducted a cross-sectional analysis of 330 patients with axSpA. Correlations among ESR, CRP, and composite disease indices were evaluated. The discriminatory capacity of each biomarker for relevant clinical thresholds was analyzed using ROC curves and optimal cut-offs identified by the Youden index. Results: ESR showed broader correlations with disease impact and activity scores than CRP. While both markers had low sensitivity overall, they were highly specific for identifying patients with very high disease activity in select scenarios. ESR ≥ 8.5 mm/h and CRP ≥ 1.88 mg/dL were strongly discriminatory in patients not exposed to biologics. CRP ≥ 0.56 mg/dL showed good performance in early disease. Conclusions: Both ESR and CRP provide complementary insights into disease activity in axSpA. ESR may offer a broader reflection of disease burden beyond inflammation. These results support a more personalized biomarker strategy in real-world axSpA management, adapted to patient profile and treatment context.