Background. According to the Third International Consensus (Sepsis-3), sepsis is defined as a life-threatening organ dysfunction caused by an uncontrolled response of the affected organism to a new infection, and septic shock as a sepsis-related condition characterized by the development of circulatory failure accompanied by arterial hypotension, with lactatemia and requiring maintenance of blood pressure with vasopressors. Despite progress in diagnosing and treating sepsis in patients with intra-abdominal infections, it continues to be the leading cause of mortality among patients in emergency departments worldwide. Purpose – the objective of this study was to ascertain the capacity of the neutrophilto-albumin ratio (NAR) before surgery to predict the severity of abdominal sepsis and 30-day mortality in patients with benign and malignant non-traumatic perforation left side of the colon. Methods. This was a retrospective, cross-sectional study that analyzed 117 patients of different age groups with sepsis caused by colon perforation who were hospitalized and operated on from January 2014 to March 2024. To evaluate the diagnostic value of INA in predicting sepsis severity and 30-day mortality, we analyzed the biomarker’s ROC curves, including the determination of optimal cut-off thresholds and associated specificity and sensitivity. The association of INA, sepsis severity, and perforation type with 30-day mortality was investigated using survival analysis, including the comparison of Kaplan–Meier curves and the development and analysis of Cox proportional hazards regression models. Comparisons between groups of study patients concerning quantitative characteristics were conducted, with the presence of septic shock and treatment outcome serving as the independent variables. This was done using nonparametric criteria for independent measurements, specifically the Kruskal–Wallis and Mann–Whitney tests. The statistical significance of the relationships between the qualitative indicators of the study was assessed based on the χ2 criterion and the odds ratio. Results. The results demonstrated that the INR has a high prognostic value in determining the severity of sepsis. This was evidenced by a high value of the area under the ROC curve (AUC = 0.948, p = 2, 309×10–41 < 0.05, 95% CI = 0.882–1.013). It has been demonstrated that the development of septic shock can be predicted by a preoperative INA value not exceeding 22.1, with the highest possible specificity (93.4%) and sensitivity (92.3%). The INA was also found to be an effective predictor of 30-day mortality in our data. The optimal INA threshold for mortality prediction was 23.8, with a specificity of 77.1 and sensitivity of 78.7% (AUC = 0.862, p = 6,072 ×10–28 < 0.05, 95% CI = 0.786-0.919). Furthermore, no statistically significant association was observed between the type of perforation and patient outcomes (χ2 = 0.00493, p = 0.944, p > 0.05). However, our study did confirm higher 30-day mortality in patients with colonic perforation in the presence of septic shock compared to patients with sepsis. Conclusions. The neutrophil-to-albumin ratio has been identified as an accurate and reliable biomarker for predicting the severity of abdominal sepsis. The biomarker demonstrated a specificity of 93.4%, a sensitivity of 92.3%, and a cut-off value of 22.1 for stratifying patients with septic shock. Furthermore, this biomarker was identified as an important predictor of 30-day mortality in both types of perforation, with an area under the ROC curve (AUC) of 0.862. Nevertheless, the value of this indicator for predicting mortality was somewhat lower than for determining septic shock. Furthermore, the results of the Cox regression analysis indicated that the impact of IA on survival was more pronounced in patients with malignant colon perforation. In patients with benign colon perforation, the model demonstrated a satisfactory fit to the input data. The presence or absence of septic shock did not influence the survival of patients in this category. The findings of the study indicated a significant correlation between INA and sepsis severity, suggesting that this indicator may serve as a straightforward prognostic tool for determining the severity of sepsis before surgery. Ultimately, the stratification of patients according to the severity of sepsis before surgery may lead to improved clinical outcomes for these patients.