Procalcitonin kinetics in critically ill patients: a retrospective analysis of the impact of renal dysfunction and renal replacement therapy

BACKGROUND: Despite its widespread use, several aspects of procalcitonin (PCT) kinetics remain unclear for guiding antibiotic therapy, particularly its behavior in acute kidney injury (AKI) and during renal replacement therapy (RRT). This study aimed to describe PCT kinetics in intensive care unit (ICU) patients with AKI, including those undergoing RRT, compared with patients without AKI. METHODS: We conducted a single-center retrospective study including 396 ICU patients. At admission, PCT, C-reactive protein (CRP), and white blood cell (WBC) count were compared across AKI stages. During ICU stay, any subsequent rise in PCT > 2 µg/L was defined as a PCT peak-episode. PCTpeak was the highest value before a sustained decline, PCTvalley the following lowest value, and PCTdecay the average daily reduction from peak to valley. Group comparisons were conducted using ANOVA or Kruskal-Wallis tests, with Bonferroni correction as appropriate. Linear mixed-effects models were applied to account for repeated measures within patients. RESULTS: CRP and WBC did not differ among AKI stages, whereas PCT increased progressively (p = 0.004). PCTpeak correlated with AKI severity (p = 0.001), while PCTdecay decreased progressively (p < 0.001). Among stage 3 patients, RRT was performed in 12.3% of cases and did not significantly affect daily PCT levels compared to non-RRT patients. CONCLUSION: AKI is associated with higher PCT peaks and reduced PCT decline, whereas RRT does not appear to significantly alter PCT kinetics.