Introduction: Total white blood cell count (WBC), erythrosedimentation rate (ESR) and C-reactive protein (CRP) are frequently used by primary care physicians attending infants < 90 days old with fever without localizing signs to distinguish those with a serious bacterial infection (SBI). The main objective of this study was to obtain the diagnostic values of these parameters in infants with fever.
Patients and methods: We analyzed previously healthy infants aged 0 to 90 days old and fever with no source of infection admitted to the emergency room and/or hospitalized. The main outcome measure was the presence or absence of a SBI (urinary tract infection, bacteremia, meningitis, pneumonia, enteritis) and diagnostic values of WBC, ESR and CRP.
Results: A total of 103 infants met the inclusion criteria. Of these, 22 infants (21.3%) had a SBI, the most common being urinary tract infection. Absolute neutrophil count (ANC) and WBC had an area under the ROC curve (AUC) of 0.6 (95% CI: 0.46-0.73) and 0.55 (95% CI: 0.44-0.68) respectively. An ANC>or=10,000/microl had a sensitivity and specificity of 9% (95% CI: 1-21) and 92.5% (95% CI: 86-98) respectively. A WBC>or=15,000/microl had a sensitivity and specificity of 13.6% (95% CI: 1-28) and 85% (95% CI: 77-93) respectively. CRP showed an AUC of 0.71 (95% CI: 0.55-0.86) and a best cut-off point of 2 mg/dL (sensitivity 53% [95% CI: 29-76] and specificity of 85% [95% CI: 75-94]). ESR>or=20 mm/hour had an AUC, sensitivity and specificity of 0.53 (95% CI: 0.37-0.7), 38% (95% CI: 16-62) and 75% (95% CI: 65-85) respectively.
Conclusions: None of these parameters alone, commonly used by physicians, is a reliable diagnostic tool to rule out SBI in infants<90 days old with fever without source of infection.