Immature neutrophils in the blood smears of young febrile children

Objective: To determine whether the immature neutrophil (band) count in the peripheral blood smear helps to distinguish young febrile children with ba cterial or respiratory viral infections. Design and Setting: A prospective cohort study in 3 pediatric emergency dep artments. Patients: A convenience sample of 100 febrile children aged 2 years or youn ger with either laboratory-documented bacterial infections (n = 31; 24 with urinary tract infections, 7 with bacteremia) or laboratory-documented resp iratory viral infections (n = 69). Each patient received a clinical appeara nce score using the Yale Observation Scale prior to laboratory evaluation. A complete blood cell count was obtained from all patients and manual diffe rential count of the peripheral blood smear was performed by 1 senior techn ician masked to clinical information. Main Outcome Measure: Band counts, represented as a percentage of white blo od cells in the peripheral blood smear, the absolute band count, and band-n eutrophil ratio. Logistic regression analysis was performed to determine wh ether the band count helps to distinguish bacterial infections from viral i nfections after adjusting for age, temperature, Yale Observation Scale scor e, and absolute neutrophil count. Results: Patients with bacterial infections had a higher mean absolute neut rophil count (11.3 vs 5.9 x 10(9)/L; P<.01) than patients with respiratory viral infections. There was no difference, however, in percentage band coun t (13.5% vs 13.3%; P = .90), absolute band count (2.2 vs 1.9 x 10(9)/L; P = .31), or band-neutrophil ratio (0.24 vs 0.33; P = .08, bacterial vs viral, respectively); the band count did not help to distinguish bacterial and vi ral infections after adjusting for age, temperature, Yale Observation Scale score, and absolute neutrophil count in the regression analysis. Conclusion: The band count in the peripheral blood smear does not routinely help to distinguish bacterial infections from respiratory viral infections in young febrile children.