In predictive models, we found IL-4 and S100A9 to be valuable markers to separate the child with ALL from JIA, with AUCs of 98% (95% CI: 98-100%) and 95% (95% CI: 91-97%), respectively, exceeding both hemoglobin, CRP, ESR and for IL-4 also platelets. Here, CRP is linked to juvenile idiopathic arthritis.