Takakura M, Shimizu M, Irabu H, et al. - For the detection of macrophage activation syndrome (MAS) complicating systemic juvenile idiopathic arthritis (s-JIA), the diagnostic accuracy of serum biomarkers (neopterin, interleukin (IL)-18, and CXCL9 and soluble tumor necrosis factor receptor type I (sTNFR-I) and II) was compared in this study including 78 patients with s-JIA, including 21 with MAS. For neopterin, IL-18, CXCL9, sTNFR-II/I ratio and ferritin, area under the curve values and cut off values generated in receiver operating characteristic curve analysis were 0.9465/19.5 nmol/l, 0.8895/69250 ng/ml, 0.9333/3130 pg/ml, 0.9395/3.796 and 0.8671/2560 ng/ml, respectively. Patients with MAS exhibited significantly high serum neopterin levels, which correlated positively with disease activity. Findings are suggestive of the possible utility of serum neopterin levels as a promising indicator of disease activity in s-JIA and MAS as well as for assessing it. It may also have utility as a marker to detect the transition to MAS from active-phase s-JIA.