Systemic Immune-Inflammation Index for the Diagnosis of Acute Appendicitis: A Systematic Review

This study aimed to analyze the systemic immune-inflammation index (SII)'s diagnostic performance in diagnosing acute appendicitis (AA) and discriminating between complicated acute appendicitis (CAA) and noncomplicated acute appendicitis (NCAA).

This review was registered in the International Prospective Register of Systematic Reviews (CRD42024587430). We included prospective and retrospective original clinical studies evaluating the diagnostic performance of SII in AA. A search was conducted in PubMed, Web of Science, Scopus, and Ovid. Search terms and keywords were the following: (appendicitis OR appendectomy) AND (systemic immune-inflammation index OR SII). Two independent reviewers selected the articles and extracted relevant data. Methodological quality was assessed using the quality assessment tool for diagnostic accuracy studies (QUADAS-2). A synthesis of the results, standardization of the metrics, four random-effect meta-analyses, and two diagnostic test accuracy (DTA) meta-analyses were performed.

Thirteen studies with data from 9083 participants, including 5255 patients with a confirmed diagnosis of AA and 3828 controls (CG), were included in this review. The random-effect meta-analysis of SII (AA versus CG) included 10 articles (3733 AA and 3510 controls) and resulted in a significant mean difference (95% CI) of 1072.46 (750.55, 1394.37; P < 0.001). The random-effect meta-analysis of SII (CAA versus NCAA) included nine articles (1116 CAA and 2984 NCAA) and resulted in a significant mean difference (95% CI) of 1294.2 (731.54, 1856.86; P < 0.001). Subgroup meta-analysis for studies conducted in pediatric-only populations maintained statistical significance. The DTA meta-analysis (AA versus CG) yielded a pooled sensitivity and specificity (95% CI) of 81.8% (75.2, 86.9) and 79.9% (68.2, 88.1). The DTA meta-analysis (CAA versus NCAA) resulted in a pooled sensitivity and specificity (95% CI) of 72.5% [49.6, 87.6] and 82.5% (65.1, 92.2). The pooled area under the curve (AA versus CG) was 0.88, and the pooled area under the curve (CAA versus NCAA) was 0.85.

SII emerges as a robust tool for diagnosing AA and differentiating between CAA and NCAA. The high meta-analytical heterogeneity, the retrospective nature of most of the included studies, and their limited geographical distribution warrant further prospective multicenter studies to validate these findings.