IL18 and adult-onset Still disease: Among the evaluated biomarkers, active IL-18 showed the highest diagnostic accuracy for AOSD (cutoff > 4,231.1 pg/mL; sensitivity, 89.4%; specificity, 92.9%; area under the curve 0.963).<h4>Conclusions</h4>Serum active IL-18 levels were significantly higher in patients with AOSD than in HCs and in patients with FMF or RA.