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

<i>Background and Objectives</i>: Procalcitonin (PCT) kinetics are increasingly used as prognostic markers in sepsis, but their interpretation is confounded by dynamic changes in renal function during acute illness. This study evaluated the prognostic value of ΔPCT for 30-day mortality in critically ill patients with either sepsis or septic shock by incorporating serial kinetic eGFR measurements and renal function-adjusted ΔPCT cut-off values based on the mean kinetic eGFR during the first 48-72 h of ICU admission. <i>Materials and Methods</i>: This retrospective cohort study included 106 adult ICU patients with either sepsis or septic shock. Serial procalcitonin measurements were used to calculate ΔPCT as a ratio of follow-up to baseline values, while renal function was assessed using mean kinetic eGFR over the first 72 h of ICU admission. <i>Results</i>: Thirty-day mortality was 43.4%. ΔPCT was a strong independent predictor of mortality across all models. At 48 h, ΔPCT2 was independently associated with 30-day mortality in the overall cohort (AUC 0.793) and demonstrated independent prognostic significance only in patients with preserved renal function (GFR ≥ 30 mL/min/1.73 m²). The optimal ΔPCT2 cut-off corresponded to a 56% reduction in procalcitonin levels. At 72 h, ΔPCT3 emerged as an independent predictor of mortality regardless of renal function. ROC analysis identified an optimal ΔPCT3 cut-off corresponding to 62% procalcitonin reduction in the overall cohort, with renal function-specific thresholds of ~50% for patients with GFR < 30 mL/min/1.73 m² and ~73% for those with preserved renal function. The combination of APACHE II score and ΔPCT3 demonstrated the highest discriminative performance for mortality prediction (AUC 0.948). <i>Conclusions</i>: Procalcitonin kinetics provide clinically meaningful prognostic information in sepsis when interpreted alongside dynamic renal function. While 48 h procalcitonin kinetics offer prognostic value primarily in patients with preserved renal function, 72 h ΔPCT provides renal function-independent and superior mortality discrimination. Integrating serial kinetic eGFR measurements enables renal function-adapted ΔPCT threshold determination and may improve risk stratification in critically ill septic patients.