Abstract
OBJECTIVE: The study aims to evaluate the diagnostic value and clinical significance of the Systemic Immune-Inflammation Index (SII) in differentiating juvenile idiopathic arthritis (JIA) from reactive arthritis (ReA) in Chinese children aged under 18. METHODS: This study conducted a retrospective analysis of 865 arthritis patients treated at Capital Children's Medical Center Affiliated to Capital Medical University between January 2020 and January 2025. Spearman correlation analysis was used to assess the relationship between SII and inflammatory biomarkers. Logistic regression analysis was performed to assess the independence of SII in JIA diagnosis, and the diagnostic performance was evaluated using receiver operating characteristic (ROC) curves. RESULTS: The diagnostic performance for differentiating JIA from ReA was evaluated using ROC curves. The area under the curve (AUC) values were as follows: SII (AUC = 0.83), c-reactive protein (CRP) (AUC = 0.81), erythrocyte sedimentation rate (ESR) (AUC = 0.78), hemoglobin (Hb) (AUC = 0.75). To statistically compare these AUC values, we implemented the DeLong test. The DeLong test results showed that the AUC of SII was significantly higher than that of CRP (p = 0.045), ESR (p = 0.012), and Hb (p = 0.003), indicating that SII is a superior predictor for differentiating JIA from ReA. Eleven biomarkers are associated with disease status, among which joint type, red cell distribution width (RDW), neutrophil count (N), platelet count (PLT), SII, platelet-to-lymphocyte ratio (PLR), and neutrophil-to-lymphocyte ratio (NLR) are identified as independent risk factors, while Hb, lymphocyte count (L), and platelet width-to-lymphocyte ratio (PWR)[platelet count ÷ white blood cell count] serve as protective factors. SII exhibits correlations with N, PLT, and L, with stronger associations observed in the JIA cohort. CONCLUSION: The SII values in JIA patients are higher than those in ReA and are associated with disease activity. This suggests that SII is applicable for early differential diagnosis between these two types of arthritis.