Juvenile Idiopathic Arthritis (JIA) is the most common chronic rheumatic disease in children. Interleukin-17A (IL-17A), a proinflammatory cytokine produced by Th17 cells, plays a key role in the pathogenesis of chronic inflammatory arthritis.

To evaluate serum IL-17A concentrations and their correlation with disease activity and inflammatory markers in children with oligoarticular and polyarticular JIA.

This cross-sectional case-control study included 40 children with oligoarticular and polyarticular JIA and 40 age and sex-matched healthy controls. Serum IL-17A concentrations were measured using enzyme-linked immunosorbent assay (ELISA). Disease activity was assessed using the Juvenile Arthritis Disease Activity Score-27 (JADAS-27). Clinical and laboratory parameters were recorded and statistically analyzed.

Serum IL-17A levels were significantly higher in patients with JIA compared with controls ( p < 0.001). Serum IL-17A showed positive correlations with JADAS-27 score ( p < 0.001), C-reactive protein ( p < 0.001), and erythrocyte sedimentation rate ( p < 0.001). ROC analysis demonstrated good discriminatory ability for IL-17A to distinguish active JIA from healthy controls (area under the curve (AUC) = 0.885, 95% confidence interval (CI): 0.816–0.954; sensitivity = 72.5%, specificity = 85.0% at a cut-off of 11.25 ng/L).

Serum IL-17A is significantly elevated in children with oligoarticular and polyarticular JIA and correlates strongly with composite disease activity and systemic inflammation. While these findings support a pathophysiological role for IL-17A-mediated inflammation in JIA, IL-17A serves as a biomarker of disease activity rather than a diagnostic tool, and the incremental clinical utility of routine IL-17A measurement beyond established inflammatory markers remains to be established.