Serum ferritin levels as a useful diagnostic marker for the distinction of systemic juvenile idiopathic arthritis and Kawasaki disease.

Objectives: The clinical features and laboratory parameters of patients with Kawasaki disease (KD) and systemic juvenile idiopathic arthritis (s-JIA) tend to overlap. Furthermore, there have been no definitive biomarkers for these diseases, making clinical diagnosis difficult. The purpose of this study was to investigate the diagnostic value of serum ferritin levels for differentiating KD from s-JIA and predicting the disease severity of KD.

Methods: We analyzed 228 patients with KD and 81 patients with s-JIA. Serum ferritin levels were compared between patients with s-JIA and KD. Furthermore, serum ferritin levels in patients with KD were compared with respect to clinical features such as responsiveness to intravenous immunoglobulin (IVIG) therapy.

Results: Serum ferritin levels in KD patients with no response to IVIG therapy were significantly higher than those in KD patients with a good response to IVIG therapy. Serum ferritin levels in patients with KD needing plasma exchange (PE) were significantly higher than those in patients not needing PE. However, serum ferritin levels overlapped between severe KD patients with nonresponsiveness to IVIG therapy or needing PE and other patients with mild KD. Furthermore, patients with s-JIA showed a distinct elevation of serum ferritin levels compared with KD patients. The cutoff value of serum ferritin levels for differentiating KD from s-JIA was 369.6 ng/ml.

Conclusions: Serum ferritin levels were significantly elevated in s-JIA patients compared with KD patients. Measurement of serum ferritin levels can be useful for differentiating s-JIA from KD.