Objectives To compare the diagnostic properties of procalcitonin (PCT), C reactive protein (CRP), total white blood cells count (WBC), absolute neutrophil count (ANC) and clinical evaluation to detect serious bacterial infection (SBI) in children with fever without source.

Design Prospective cohort study.

Setting Paediatric emergency department of a tertiary care hospital.

Participants Children aged 1–36 months with fever and no identified source of infection.

Intervention Complete blood count, blood culture, urine analysis and culture. PCT and CRP were also measured and SBI probability evaluated clinically with a visual analogue scale before disclosing tests results.

Outcome measure Area under the curves (AUC) of the receiver operating characteristic curves.

Results Among the 328 children included in the study, 54 (16%) were diagnosed with an SBI: 48 urinary tract infections, 4 pneumonias, 1 meningitis and 1 bacteraemia. The AUC were similar for PCT (0.82; 95% CI 0.77 to 0.86), CRP (0.88; 95% CI 0.84 to 0.91), WBC (0.81; 95% CI 0.76 to 0.85) and ANC (0.80; 95% CI 0.75 to 0.84). The only statistically significant difference was between CRP and ANC (Δ AUC 0.08; 95% CI 0.01 to 0.16). It is important to note that all the surrogate markers were statistically superior to the clinical evaluation that had an AUC of only 0.59 (95% CI 0.54 to 0.65).

Conclusion The study data demonstrate that CRP, PCT, WBC and ANC had almost similar diagnostic properties and were superior to clinical evaluation in predicting SBI in children aged 1 month to 3 years.