The Role of Emerging Immune-Inflammatory Indexes in the Preoperative Differentiation of Complicated and Uncomplicated Acute Appendicitis: A Single-Center Retrospective Analysis

<b>Background/Objectives</b>: Acute appendicitis (AA) is among the most common surgical emergencies. Differentiating between complicated (CAA) and uncomplicated (UAA) forms is essential for selecting the appropriate management-operative or non-operative-and for optimizing patient prioritization and outcomes. This study aimed to evaluate the diagnostic performance of emerging inflammatory indices in distinguishing these forms of AA. <b>Methods</b>: A total of 514 adult patients with surgically confirmed AA were retrospectively analyzed. Six immune-inflammatory indices-neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), and pan-immune-inflammation value (PIV)-were calculated and compared with intraoperative and histopathological findings. Postoperative outcomes, including length of hospital stay (LOS) and hospitalization costs, were also evaluated. <b>Results</b>: All six indices were significantly higher in intraoperatively identified complicated cases (<i>p</i> < 0.0001). In histopathological analysis, five indices (NLR, MLR, SII, SIRI, and PIV) remained significantly elevated in patients with wall necrosis or perforation (<i>p</i> = 0.000-0.019), while PLR did not reach statistical significance. The indices showed fair diagnostic accuracy (AUC = 0.664-0.719, <i>p</i> < 0.0001). NLR and MLR were independent risk factors for CAA (<i>p</i> = 0.006 and <i>p</i> = 0.016), and MLR was also independently associated with complicated histopathological findings (<i>p</i> = 0.036). PIV independently predicted both increased LOS and higher hospitalization costs (<i>p</i> = 0.001 for each). <b>Conclusions:</b> These easily calculable inflammatory markers can serve as useful adjuncts for preoperative stratification of AA, supporting timely decision-making and contributing to more cost-effective emergency surgical care.