Serum Procalcitonin versus C-Reactive Protein for Discriminating Serious Bacterial Infection in Febrile Infants Under 90 Day

Abstract

Febrile infants under 90 days of age are at elevated risk of serious bacterial infection (SBI), yet the majority have self-limiting viral illness. Distinguishing the two at presentation governs decisions on lumbar puncture, empirical antibiotic therapy, and hospital admission. To compare the diagnostic accuracy of serum PCT and CRP, alone and combined with clinical assessment, for discriminating culture-confirmed SBI from viral or non-bacterial febrile illness in infants under 90 days. A prospective single-center diagnostic-accuracy cohort study was conducted at pediatric department of Bint AlHuda teaching hospital from 1 February 2024 through 1 October 2025 and reported in accordance with the Standards for Reporting of Diagnostic Accuracy Studies (STARD) 2015 statement. Consecutive febrile infants under 90 days undergoing a full sepsis evaluation had paired PCT and CRP measured at presentation, before antibiotic administration. The reference standard was culture-confirmed SBI (blood, urine, or cerebrospinal fluid) supplemented by structured clinical adjudication. Of 458 infants assessed, 348 formed the analytic cohort; SBI was confirmed in 71 (20.4%), of which urinary tract infection was the most frequent (62.0%). PCT achieved an AUC of 0.86 (95% confidence interval [CI] 0.80–0.92) versus 0.78 (95% CI 0.71–0.85) for CRP (DeLong p = 0.018). At a cut-off of 0.5 ng/mL, PCT sensitivity was 88.7% and specificity 74.1%; a combined PCT + CRP + clinical model reached AUC 0.90 (95% CI 0.85–0.95). PCT outperformed CRP for discriminating SBI in febrile infants under 90 days and added incremental value to clinical assessment, supporting its incorporation into risk-stratification pathways where available.