Comparative Prognostic Value of Ion Shift Index and Naples Prognostic Score for Predicting In-Hospital Mortality in STEMI Patients: A Single-Center Retrospective Study

<b>Background/Objectives:</b> Acute myocardial infarction with ST-segment elevation (STEMI) remains a clinical condition with high mortality. The Ion Shift Index (ISI) and Naples Prognostic Score (NPS) are two prognostic indicators that have recently come to the fore. The aim of this study is to compare the predictive value of ISI and NPS in predicting in-hospital mortality in STEMI patients. <b>Methods:</b> This retrospective study included 214 STEMI patients (1 January 2022-1 January 2024). Exclusion criteria included active cancer, infection, autoimmune disease, or chronic kidney disease. ISI and NPS were calculated from laboratory results obtained from the emergency department at the time of initial presentation. Patients were categorized according to in-hospital survival. Logistic regression and ROC curve analyses were performed for in-hospital mortality. <b>Results:</b> The mean age of participants was 64.8 ± 11.2 years, and 40.2% were female; a total of 36 patients (16.8%) died during hospitalization. Hypertension and female gender were more common in those who died, and LDL cholesterol and inflammatory markers were higher. The ISI value was significantly increased in the mortality group, whereas no significant difference was observed in NPS. ROC analysis revealed that at a threshold value of 3.0, ISI had a sensitivity of 68% and specificity of 71%, with an area under the curve (AUC) of 0.70, while NPS had an AUC of 0.55 and did not demonstrate significant discriminatory power. In the multivariate analysis, ISI and increased LDL cholesterol were independently associated with mortality; decreased lymphocyte/monocyte ratio and female gender were also additional independent predictors. NPS did not emerge as an independent factor in predicting in-hospital mortality. <b>Conclusions:</b> ISI was found to be a superior and independent early risk predictor of in-hospital mortality in STEMI patients compared to NPS. ISI may serve as a rapid and inexpensive risk classification tool in the acute phase, as it reflects sudden changes in intracellular-extracellular ion balance, whereas NPS may not be sufficiently sensitive in the hyperacute phase, as its components reflect chronic nutritional and inflammatory states. Due to limitations such as a single-center retrospective design and low mortality rates, validation through multicenter prospective studies is required for the integration of ISI into clinical practice.