TNF and juvenile idiopathic arthritis: Of the serum biomarkers with higher levels in JIA compared to controls (positive NPX values), TNF had the most pronounced difference in mean NPX value of 1.04, followed by S100A12, fibroblast growth factor 21 (FGF21), and CC motif chemokine ligand 20 (CCL20) with differences of more than 0.5.