Procalcitonin as a Severity-Based Risk Stratification Marker in Pediatric Infectious Diarrhea: A Prospective Study from the Emergency Department

<b>Objectives</b>: Procalcitonin (PCT) is used increasingly in emergency settings to guide evaluation of febrile illnesses, but its role in pediatric infectious diarrhea, particularly as a marker of severity, remains unclear. The study objective evaluates whether PCT correlates with clinical severity and outcomes in pediatric infectious diarrhea presenting to the emergency department (ED). <b>Methods</b>: This prospective study enrolled 105 children with infectious diarrhea presenting to a tertiary pediatric ED. Serum PCT, C-reactive protein, clinical features, hydration status, treatment decisions (including hospitalization and antibiotic use), and outcomes were analyzed. PCT cutoffs (<0.25, <0.5, and <1.0 ng/mL) were evaluated for their associations with Salmonella infection and severity measures, including dehydration, hospitalization, length of stay, and antibiotic use. <b>Results</b>: Thirty-five patients (33.3%) had Salmonella enteritidis. PCT levels did not differ significantly between Salmonella-positive and negative cases (median 0.49 vs. 0.46 ng/mL; <i>p</i> = 0.84), and PCT demonstrated poor diagnostic performance (AUC 0.49). In contrast, PCT was strongly associated with markers of severity. Compared with lower PCT levels, children with PCT ≥ 0.25 ng/mL were more frequently hospitalized (92.1% vs. 52.6%; <i>p</i> < 0.001) and had longer hospital stays (4.41 vs. 3.00 days; <i>p</i> < 0.001). Higher PCT levels were also associated with more dehydration, higher CRP (all <i>p</i> < 0.001), and greater antibiotic use (66.7% vs. 23.7%; <i>p</i> < 0.001). PCT thresholds of 0.25-0.5 ng/mL consistently identified children at increased risk for admission and higher treatment intensity. <b>Conclusions</b>: PCT should not be used as a diagnostic marker for Salmonella enteritidis. Instead, it reflects the host inflammatory response and is strongly associated with clinical severity in children with acute infectious diarrhea evaluated in the ED. The incorporation of PCT thresholds into ED assessment may support early severity-based risk stratification and inform decisions regarding admission and treatment intensity.