Background and aims To evaluate the diagnostic usefulness of biomarkers in the management of children with fever at risk of serious bacterial infections (SBI) at the emergency department (ED).

Methods In this prospective observational study previously healthy children with fever, aged 1 month to 16 years, attending the EDs of a university hospital and a teaching hospital (Rotterdam, the Netherlands) between 2009 and 2012 were included. Standardised information on clinical signs and symptoms, C-reactive protein (CRP), procalcitonin (PCT), neutrophil CD64 expression and urinalysis were collected prospectively. Logistic multivariable regression analysis was used to assess diagnostic performance.

Results 1,084 children were included, median age was 1.6 years (interquartile range: 0.8–3.5), 170 children (16%) had SBI. CRP (receiver operating characteristic curve (ROC-area) 0.77 (95% confidence interval (CI) 0.69–0.85)) and PCT (ROC-area 0.75 (95% CI 0.67–0.83)) were both strong predictors of SBI. CD64 lacked diagnostic strength (ROC-area 0.62 (95% CI 0.54–0.70)). A score containing PCT and CRP together with urinalysis, the Lab-score, performed well (ROC-area 0.79 (95% CI 0.72–0.87)), but thresholds performed similar to often used cut-offs of single biomarkers. Combined with clinical signs and symptoms both CRP and PCT were useful; additional PCT to CRP did not improve diagnostic performance substantially.

Conclusions CRP and PCT were equally useful in the diagnostic evaluation of the febrile child, whereas CD64 wasn’t useful. Performing both CRP and PCT is often not indicated in a general population of febrile children. Our findings contrast previous studies suggesting PCT outperforming CRP and superior value of CD64 in specific settings.