Juvenile idiopathic arthritis is a common pediatric rheumatologic disease, and the mainstay of treatment is immunosuppressive medication. The most problematic complication of immunosuppression is infection. Distinguishing the inflammation of immune flares with that of infections can be very challenging, particularly in systemic JIA (sJIA), where signs and symptoms are similar. In this study, we propose using two markers in the blood, procalcitonin and calprotectin, to distinguish disease flare and infection in children with sJIA. In order to achieve this, we will draw blood from children with sJIA at two timepoints, when blood is being drawn anyway as part of standard of care. We anticipate that procalcitonin will be elevated in children with infection, and calprotectin will be elevated in children with disease flare, so that the combination of these two markers will give very valuable information together. This will allow more accurate and early diagnosis to direct proper treatment.