S100A9 and systemic-onset juvenile idiopathic arthritis: In the present study, the serum concentrations of IL-6, IL-18, S100A8, and S100A9 were measured and comparatively analyzed in pediatric patients with sJIA and other diseases that can be easily misdiagnosed as sJIA, including acute lymphoblastic leukemia (ALL), severe infections (SIF), KD, and juvenile idiopathic arthritis (JIA) with multiple joint involvement.