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Background: Juvenile idiopathic arthritis (JIA) is among the most common autoimmune diseases in children, yet its pathophysiology remains incompletely understood. Reliable biomarkers are needed to assess disease activity and guide therapy. Bile salt-stimulated lipase (BSSL), originally identified as a lipolytic enzyme, has recently been implicated in inflammatory conditions such as rheumatoid arthritis (RA) and psoriatic arthritis (PsA) in adults. Elevated serum BSSL levels correlate with markers of inflammation and decrease following positive response to anti-inflammatory treatments, suggesting potential utility as both a biomarker and a therapeutic target.

Methods: Serum BSSL concentrations were measured in children with JIA and compared with healthy controls. Correlations between BSSL and inflammatory markers (S100A8/A9, HNL), blood cell counts (leukocytes, neutrophils, platelets), and clinical disease-activity indices (ESR, JADAS27, cJADAS27, CHAQ) were evaluated.

Results: Children with JIA had significantly higher serum BSSL concentrations than healthy controls, and levels decreased following medical treatment. BSSL correlated positively with platelets, ESR, and S100A8/A9, but not with JADAS27.

Conclusion: Serum BSSL tracks systemic inflammatory activity and decreases with clinical improvement in JIA, supporting its further evaluation as a complementary inflammatory biomarker and potential pharmacodynamic read out in pediatric inflammatory arthritis.