Evaluation of Acute Pancreatitis Severity and Prognosis Using the Aggregate Systemic Inflammation Index (AISI) as a New Marker: A Comparison with Other Inflammatory Indices

<b>Background/Objectives:</b> Acute pancreatitis (AP) remains a pressing clinical challenge, largely due to its potential to lead to life-threatening complications and increased mortality. Over the years, numerous tools have been proposed to evaluate the intensity of AP and estimate likely health outcomes. Despite their usefulness, many of these assessment models are complex and rely on a wide array of clinical inputs, making them less practical in everyday healthcare settings. In contrast, the Aggregate Systemic Inflammation Index (AISI), which is calculated using routine blood count parameters, provides a simpler and more inclusive approach to measuring systemic inflammation. This research focuses on examining how effectively AISI can be used to gauge disease severity and project clinical trajectories in individuals affected by pancreatitis. <b>Methods:</b> This retrospective study reviewed the medical records of 412 individuals diagnosed with acute pancreatitis, all of whom received care at the Internal Medicine Clinic of Ankara Bilkent City Hospital between 1 April 2019 and 1 September 2024. The investigation encompassed a thorough analysis of patients' demographic characteristics, lab parameters, and clinical findings, with special attention given to inflammatory markers, including the Aggregate Systemic Inflammation Index (AISI), its revised version, the Platelet-to-Lymphocyte Ratio (PLR), the Neutrophil-to-Lymphocyte Ratio (NLR), and the Systemic Inflammatory Response Index (SIRI). Comparative analyses between groups were performed using independent sample <i>t</i>-tests and one-way ANOVA, complemented by Tukey's post hoc tests where appropriate. Correlations among continuous variables were determined through Pearson's analysis, and the prognostic accuracy of both AISI and its modified form was assessed using Receiver Operating Characteristic (ROC) curve methodology. <b>Results:</b> The mean age among participants was 63.47 ± 17.92 years, while the average AISI value was calculated as 1183.89 ± 1067.42. Both the original and modified versions of the AISI index showed strong positive correlations with several key clinical measures, including prolonged hospitalization, a Glasgow score of 2 or above, BISAP, Ranson scoring, the revised Atlanta classification, and APACHE II. AISI was also significantly linked to the presence of complications and overall mortality (<i>p</i> < 0.01). Analysis through ROC curves demonstrated that an AISI level above 236.626 effectively predicted hospital stays exceeding 10 days, with a sensitivity of 94.40% and a specificity of 91.00%. Moreover, both AISI and its modified form reliably distinguished patients who had a Ranson score of zero, with high diagnostic accuracy. <b>Conclusions:</b> AISI and its modified version demonstrate a strong association with both the intensity and clinical course of acute pancreatitis. Thanks to their simplicity, low cost, and broad usability in healthcare settings, these indices hold considerable promise as practical and dependable tools for assessing the severity and likely outcomes of this increasingly prevalent disease.