Procalcitonin kinetics in critically ill children: impact of continuous kidney replacement therapy modality and dose

BACKGROUND: Acute kidney injury (AKI) is common in critically ill children, frequently necessitating continuous kidney replacement therapy (CKRT). Procalcitonin (PCT) is widely used as an infection biomarker, yet its interpretation during CKRT remains unclear. Adult data regarding extracorporeal clearance of PCT are inconsistent, while pediatric evidence is limited. METHODS: In this prospective observational study (May 2021-October 2023), 40 critically ill children receiving CKRT in a tertiary PICU were enrolled. Serum PCT was measured at CKRT initiation (T0), 12 h (T12), and 24 h (T24). CKRT modalities (CVVH, CVVHD, CVVHDF), effluent doses, and membrane types (PS, PAES, AN69-ST) were recorded. PCT kinetics were analyzed using non-parametric tests, with correlation assessed by Spearman's rank. RESULTS: Median baseline PCT was 3.6 ng/mL (IQR 0.5-27.2), rising to 7.4 (0.6-29.5) at T12 and stabilizing at 7.7 (0.6-30.5) at T24. Differences across time points were not statistically significant (p = 0.68). PCT trajectories were unaffected by CKRT modality, effluent dose, or membrane type, and no correlation was found between effluent dose and PCT changes. Stratification by high versus low effluent dosing revealed no significant differences. CKRT-related complications occurred in 17.5%, mainly filter clotting, without influencing PCT. PICU mortality was 35%, reflecting illness severity rather than CKRT. CONCLUSIONS: In pediatric CKRT, short-term PCT dynamics are driven by the underlying septic or inflammatory process rather than CKRT parameters. PCT typically peaks within 12 h of CKRT initiation and then stabilizes, supporting its reliability for infection monitoring and antibiotic stewardship during early CKRT. Larger studies are warranted to define long-term PCT behavior and prognostic utility.