Immature neutrophils in young febrile infants

Background: To describe the diagnostic value of the absolute band count (ABC) and ratio of immature to total neutrophils (I:T) for invasive bacterial infections (IBIs; bacterial meningitis and bacteraemia) among young febrile infants. Methods: We performed a cross-sectional study in a paediatric emergency department of febrile infants ≤60 days over 12 years to evaluate the accuracy of the ABC and I:T for IBI. Results: Of 2930 included patients, 75 (2.6%) had IBIs. The area under the curve (AUC; 95% CI) for ABC was 0.69 (0.62 to 0.76) with sensitivity 0.27 (0.17 to 0.38) and specificity 0.94 (0.93 to 0.95) at cutoff ≥1500 cells/μL. The AUC for I:T was 0.65 (0.59 to 0.72) with sensitivity 0.29 (0.19 to 0.41) and specificity 0.88 (0.87 to 0.89) at cutoff ≥0.2. Only the ABC in infants 29-60 days was minimally accurate. Conclusion: The ABC and I:T were generally inaccurate for detecting IBI in febrile infants. Guidelines without these parameters may be better for risk assessment.