The Role of the Systemic Immune-Inflammation Index in Predicting Hospitalization in Children with Acute Gastroenteritis

Objective: Acute diarrhea in childhood is one of the most common infections in children and a leading cause of death from infectious diseases under five years of age worldwide. The Systemic Immune-Inflammation Index (SII) reflects the balance between inflammation and immune response. This study aimed to investigate the relationship between acute gastroenteritis (AGE) infection and SII in children. Methods: This retrospective study included 3,039 children, comprising 1,668 with AGE and 1,371 healthy controls. Hematologic parameters and SII were analyzed. Data was compared across patient and control groups, inpatients versus outpatients, and groups with viral versus parasitic AGE etiologies. Results: Of the participants, 1,335 (43.9%) were female and 1,704 (56.1%) were male. Among the AGE cases, 116 (7.0%) required hospitalization, while the remainder were managed as outpatients. The median length of hospital stay among inpatients was 2.0 days (interquartile range 1.0). In AGE patients, white blood cell count, neutrophil count, platelet count, SII, neutrophil-to-lymphocyte ratio (NLR), and platelet count-to-lymph ratio (PLR) were significantly higher, while lymphocyte and eosinophil counts were significantly lower compared with controls (p < 0.001 for all). In outpatients, leukocyte, neutrophil, SII, NLR, and PLR were significantly higher, and lymphocyte count significantly lower than in inpatients (all p < 0.001). For AGE patients, the SII cut-off value for predicting hospitalization was ≤ 802.11, yielding a sensitivity of 65.3% and specificity of 71.6%. For distinguishing AGE patients from controls, the SII cut-off value was ≥ 628.70, with a sensitivity of 71.0% and specificity of 81.8%. Conclusion: In children with AGE and among those treated as outpatients, NLR, PLR, and SII were elevated. We identified an SII cut-off value for predicting hospitalization in AGE patients. Further large, prospective studies are warranted to validate these findings.