Prognostic value of admission ionized calcium for short-term mortality in critically Ill children with sepsis: a single-center retrospective cohort study.

Background: Sepsis remains a leading cause of morbidity and mortality among critically ill children admitted to pediatric intensive care units (PICUs). Early risk stratification at admission is essential but is often limited by the complexity and delayed availability of existing severity scoring systems. Disturbances in calcium homeostasis, particularly hypocalcemia, are common in critical illness; however, the prognostic significance of admission serum ionized calcium (iCa) for short-term mortality in pediatric sepsis has not been well defined. Methods: This single-center retrospective cohort study analyzed data from the Pediatric Intensive Care database of the Children's Hospital affiliated with Zhejiang University School of Medicine (2010-2019). Children with sepsis who had iCa measurements within 24 h of PICU admission were included. Hypocalcemia was defined as iCa < 1.15 mmol/L. The primary outcome was 28-day all-cause mortality. Kaplan-Meier analysis and Cox proportional hazards models were used to assess the association between iCa and mortality. Discriminatory performance and incremental prognostic value were evaluated using receiver operating characteristic (ROC) curves, integrated discrimination improvement (IDI), and net reclassification improvement (NRI). Subgroup analyses and interaction tests were performed to assess the consistency of the association between iCa and mortality across predefined strata of disease severity. Results: A total of 289 children were included, among whom 26 (9.0%) died within 28 days. Hypocalcemia at admission was common (50.8%) and was associated with significantly higher mortality compared with normocalcemia (19.2% vs. 3.4%; log-rank Conclusions: Lower admission iCa levels are independently associated with higher 28-day mortality in pediatric sepsis, particularly in the early phase of illness. As a rapid and routinely available biomarker, iCa may enhance early risk stratification in critically ill children with sepsis.