Evaluating C-Reactive Protein and Procalcitonin Discordance Among Febrile Infants at Risk of Serious Bacterial Infections

Abstract

Aim

We aimed to investigate the prevalence and factors associated with C-reactive protein (CRP) and procalcitonin (PCT) discordance in febrile infants with serious bacterial infections (SBIs).

Methods

We performed a retrospective review of febrile infants ≤ 90 days old presenting to the emergency department between December 2018 and June 2023. We compared conservative and pragmatic thresholds for PCT (< 0.5 ng/mL and < 1.7 ng/mL) and CRP (< 10 mg/L and < 20 mg/L). Discordance was defined as normal CRP with abnormal PCT and vice versa. Performance was presented using sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV).

Results

Among 3459 infants, 426 infants (12.3%) had SBIs, among whom 355 (83.3%) had both CRP and PCT performed. Overall, a conservative CRP threshold had the highest sensitivity (74.1%, 95% CI 69.2%–78.6%) and NPV (95.6%, 95% CI 94.6%–96.4%). Among those with SBIs, 148/355 (41.7%) had a normal PCT (< 1.7 ng/mL) and an abnormal CRP (≥ 20 mg/L), while 16/355 (4.5%) had a normal CRP (< 20 mg/L) and an abnormal PCT (≥ 1.7 ng/mL). An increased discordance, specifically abnormal CRP with normal PCT, was found in males, infants 29–90 days old, and those with urinary tract infections.

Conclusion

SBI clinical decision rules should consider CRP-PCT discordance in specific patient populations.