Objective To determine the relationship between near-patient-test (NPT) lactate, white blood cell count (WBC) and C-reactive protein (CRP) and severe bacterial infection (SBI) in children presenting to the emergency department (ED) with infection.

Methods An observational cohort study was undertaken in a paediatric emergency department of a large urban teaching hospital. Data were collected from January 2007 until December 2007. Inclusion criteria were age <16 years, blood test including NPT lactate obtained in the ED and infection-related ED diagnosis. Patients were pre-assigned to risk groups according to their NPT lactate, WBC and CRP.

Results 506 children were included in the study, of which 42 (8.3%) had SBI. NPT lactate, WBC and CRP were significantly higher in the SBI cohort. High-risk NPT lactate (≥4 mmol/l) had a sensitivity of 38.1% (95% CI 23.6% to 54.4%) and a specificity of 89.7% (95% CI 86.5% to 92.3%); high-risk WBC (<5 or ≥15×10⁹/l) had a sensitivity of 51.2% (95% CI 35.1% to 67.1%) and a specificity of 73.8% (95% CI 69.4% to 77.8%); and high-risk CRP (≥50 mg/l) had a sensitivity of 36.8% (95% CI 21.8% to 54.1%) and a specificity of 83.6% (95% CI 79.4% to 87.2%) for SBI. All three high-risk markers combined yielded a sensitivity of 5.3% (95% CI 1.5% to 17.3%) and a specificity of 99.2% (95% CI 97.6% to 99.7%) for SBI.

Conclusion The data from our study suggest that NPT lactate provides early diagnostic information about the risk of SBI in children presenting to the ED with a suspected infection. Combining NPT lactate with WBC and CRP resulted in a promising rule-in-tool for SBI in children in the ED which, with prospective validation, has the potential to aid early identification of SBI in children.