IL18 and macrophage activation syndrome: Interestingly, our data reveal an increase in IL‐18 levels during the month preceding MAS, similar to ferritin levels, with IL‐18 levels peaking at diagnosis of MAS (from median 4,222 pg/mL [IQR 2,184–30,017 pg/mL] one month before diagnosis to 58,141 pg/mL [IQR 13,941–222,273 pg/mL] at MAS diagnosis; P = 0.011).