Diagnostic superiority of serial increase in C-reactive protein versus single measurement in differentiating bacterial from non-bacterial etiologies in pediatric patients.

Background: The diagnostic value of a single C-reactive protein (CRP) measurement in distinguishing bacterial from non-bacterial infections is limited. CRP velocity (CRPv), a dynamic metric derived from sequential CRP measurements, has shown promise in enhancing diagnostic accuracy in adults. Aims: To evaluate the association between CRPv in the first 24 hours of presentation and bacterial etiologies in pediatric patients with initial CRP level < 31.9 mg/L on presentation to the pediatric emergency department (PED). Methods: A retrospective cohort analysis of patients under 18 years of age who presented to our emergency department from 2018 through 2021. Each patient had two CRP measurements within a 24-hour period. CRPv was computed as the difference between the first (CRP1) and second (CRP2) CRP values divided by the time interval between measurements. Bacterial infections were determined based on discharge diagnoses, including positive cultures or clinical/radiological evidence. Results: Of 307 patients with initial CRP1 ≤ 31.9 mg/L, 103 (33.5%) were diagnosed with bacterial infections. Patients with bacterial infections had significantly higher CRP1, CRP2, and CRPv values. CRPv showed the highest area under the curve (AUC) and was the strongest independent predictor of bacterial infection, with an adjusted odds ratio of 2.8 (95% CI 1.3 to 6.0, Conclusions: CRPv provides superior diagnostic accuracy compared to single CRP measurements in identifying bacterial infections in pediatric patients with low initial CRP levels, suggesting its potential for enhancing early detection and guiding treatment. Further prospective studies are needed to confirm its clinical utility.