Compositions and methods for diagnosing and differentiating systemic juvenile idiopathic arthritis and Kawasaki disease

A method for diagnosing and treating systemic Juvenile Idiopathic Arthritis (sJIA) flare in a subject, the method comprising the steps of:

• (i) determining the expression level of each of a plurality of biomarkers in a blood or plasma sample obtained from the subject, wherein the plurality of biomarkers comprises Calprotectin, Follistatin-related protein (FSTL-1), C Reactive Protein (CRP) and Serum Amyloid P (SAP;
• (ii) providing a diagnosis of sJIA flare in the subject if the expression level of Calprotectin is higher compared to the expression level in healthy control subjects or a subjects with febrile illness, the expression level of FSTL-1 is higher compared to the expression level in healthy control subjects, subjects with febrile illness or a subjects with Kawasaki disease, the expression level of CRP is lower compared to the expression level in subjects with Kawasaki disease, and the expression level of SAP is lower compared to the expression level in subjects with febrile illness or Kawasaki disease;
• and
• (iii) treating sJIA flare in the diagnosed subject with an agent selected from the group consisting of nonsteroidal anti-inflammatory drugs (NSAIDs), disease modifying anti-rheumatic drugs (DMARDs), biologic agents selected from anti-IL-6 therapy and interleukin-1 receptor antagonist therapy, and intra-articular and oral steroids.