Impact of Procalcitonin Kinetics on Mortality in Intensive Care Patients with Sepsis

Background and Objectives: Procalcitonin (PCT) kinetics have emerged as a promising prognostic marker in sepsis; however, their interpretation is complicated by dynamic changes in renal function during acute illness. Most previous studies relied on a single baseline estimated glomerular filtration rate (eGFR), which may lead to misclassification in patients with evolving acute kidney injury. This study aimed to evaluate the prognostic value of procalcitonin kinetics (ΔPCT) for 30-day mortality in critically ill patients with sepsis or septic shock by incorporating serial kinetic eGFR measurements and renal function–adapted ΔPCT cut-off values based on the mean kinetic eGFR during the first 72 hours of intensive care unit (ICU) admission. Materials and Methods: This retrospective cohort study included 106 adult patients admitted to a general ICU with sepsis or septic shock. Procalcitonin levels were measured serially, and ΔPCT was calculated as the logarithmic ratio of follow-up to baseline values. Renal function was assessed using kinetic eGFR calculated at serial time points from ICU admission, and the mean kinetic eGFR over the first 72 hours was used for renal function stratification. Multivariable logistic regression models incorporating ΔPCT and severity scores (APACHE II and SOFA) were constructed, and discriminative performance was evaluated using receiver operating characteristic (ROC) curve analysis. Results: Thirty-day mortality was 43.4%. ΔPCT was a strong independent predictor of mortality across all models. When stratified according to mean kinetic eGFR, optimal ΔPCT cut-off values expressed as absolute proportional PCT decline differed markedly by renal function: an 81.2% decrease in PCT best discriminated mortality in the overall cohort, whereas renal function–specific thresholds were 63.7% for patients with mean kinetic eGFR <30 mL/min, 87.6% for those with kinetic eGFR 30–59 mL/min, and 92.6% for patients with kinetic eGFR ≥60 mL/min. The combination of APACHE II and ΔPCT demonstrated the highest discriminative performance (AUC 0.946). Conclusions: Procalcitonin kinetics provide robust prognostic information in sepsis when interpreted alongside dynamic renal function. Using serial kinetic eGFR measurements and the 72-hour mean renal function enables renal function–adapted ΔPCT cut-off determination and may improve mortality risk stratification in critically ill septic patients.