Clinical significance of the systemic immune-inflammation index in relation to pathology, treatment and outcomes in acute appendicitis: a retrospective study.

INTRODUCTION: Acute appendicitis is a common abdominal emergency. Systemic Immune-Inflammation Index (SII) is a biomarker reflecting immune status and inflammatory response, but its role in acute appendicitis remains poorly characterized. This study aims to investigate the potential diagnostic and therapeutic value of SII for assessing infection severity and prognosis in acute appendicitis. MATERIALS AND METHODS: This retrospective study analyzed clinical data from patients with acute appendicitis admitted to our hospital. The SII was the primary exposure variable and calculated as SII = platelet count × neutrophil count /lymphocyte count. Outcome variables included length of stay and total hospitalization costs. Covariates included age, sex, admission time, body temperature, shock status, comorbidities, hemoglobin, procalcitonin, presence of fecalith on computed tomography (CT), placement of intraoperative drainage tubes, and postoperative pathological classification. RESULTS: The study included 2,458 patients with acute appendicitis. Surgically treated patients had significantly higher SII than conservatively managed patients (2077.76 vs. 1526.80). SII was positively correlated with the pathological severity of acute appendicitis (p < 0.001). Patients with gangrenous appendicitis had a significantly higher SII values [median 2452.10 (IQR 1486.70-3920.70)] than those with simple inflamed appendicitis [median 1026.14 (IQR 505.86-1501.76)]. Moreover, SII was significantly associated with intraoperative drainage tube placement (p = 0.002); patients in the drainage tube group had higher SII values [median 2263.32 (IQR 1326.86-3682.69)] than those in the non-drainage tube group [median 1977.62 (IQR 1121.81-3409.83)]. CONCLUSIONS: SII is a valuable diagnostic tool in patients with acute appendicitis, offering a quantitative basis for clinical decision-making.