Prognostic Role of Third-Day CRP, Lactate and MechanicalVentilation in Predicting ICU Mortality in Sepsis: A Single-Center Study

Background Sepsis remains a leading cause of morbidity and mortality in intensive care units (ICUs). Early identification of high-risk patients is essential for optimizing management. While C-reactive protein (CRP), procalcitonin (PCT), and lactate are widely used biomarkers, evidence on the prognostic value of their dynamic changes, particularly on the third day of ICU stay, is limited. This study aimed to evaluate the prognostic role of third-day CRP, lactate, and mechanical ventilation requirement in predicting 30-day mortality in septic ICU patients. Methods We conducted a retrospective cohort study of adult patients with sepsis admitted to the ICUs of Mersin City Training and Research Hospital between January 2018 and December 2023. Patients younger than 18 years, those with incomplete data, early deaths within 24 hours, and recurrent admissions were excluded. Clinical and laboratory parameters were recorded at admission and on the third day. The primary outcome was all-cause 30-day mortality. Multivariable logistic regression was used to identify independent predictors, and model performance was assessed using receiver operating characteristic (ROC) analysis. Results A total of 200 patients were included (mean age 68.5 years; 55% male). The 30-day mortality rate was 41.5%. Baseline APACHE II and SOFA scores were not predictive of mortality. By contrast, third-day CRP and lactate levels were significantly higher in non-survivors (18.0 ± 11.7 vs. 9.1 ± 7.2 mg/dL, p < 0.001; 3.22 ± 2.58 vs. 1.73 ± 0.81 mmol/L, p < 0.001, respectively). Mechanical ventilation was required in 67.1% of non-survivors compared with 4.3% of survivors (p < 0.001). In multivariable analysis, third-day CRP (OR 1.10, 95% CI 1.04–1.17), third-day lactate (OR 2.10, 95% CI 1.36–3.24), and mechanical ventilation (OR 42.9, 95% CI 12.9–143.0) remained independent predictors. The combined model demonstrated excellent discriminatory ability (AUC = 0.919; sensitivity = 84.1%; specificity = 84.6%). Conclusion Third-day CRP and lactate levels, together with mechanical ventilation requirement, provide a robust and clinically applicable model for predicting 30-day mortality in septic ICU patients. Incorporating dynamic biomarkers into prognostic assessment may improve early risk stratification, guide timely treatment, optimize ICU resource use, and support palliative care decisions. Conclusion Third-day CRP and lactate levels, together with mechanical ventilation requirement, provide a robust and clinically applicable model for predicting 30-day mortality in septic ICU patients. Incorporating dynamic biomarkers into prognostic assessment may improve early risk stratification, guide timely treatment escalation, optimize ICU resource allocation, and support palliative care decisions in appropriate cases. These findings highlight the value of combining laboratory and clinical parameters in the prognostic evaluation of sepsis