Peripheral leukocyte count and leukocyte indexes in healthy newborn term infants

Purpose: This study was designed to determine normal values for the peripheral leukocyte count and leukocyte indexes in healthy term neonates at a specific time after birth. Methods: We prospectively enrolled 193 healthy term-gestation neonates with no identifiable perinatal risk factors for sepsis. At 4 hours of age a blood sample was collected by warmed heel stick. An automated Coulter complete blood cell count and a 100-cell manual differential leukocyte count were performed on each sample. The differential count was performed by a single hematopathologist unaware of the clinical status of each infant. Perinatal factors were identified by review of the mothers' and infants' hospital records. Results: The mean ratio of immature to total neutrophils was 0.16 (SD 0.10), and the 10% to 90% range was 0.05 to 0.27. The mean leukocyte count was 24.06 × 10⁹/L (24,060/mm³), and the 10% to 90% range was 16.2 to 31.5 × 10⁹/L (16,200 to 31,500/mm³). Neutropenia, <1.5 × 10⁹/L (1500/mm³) segmented plus band form neutrophils, was not observed. Of all the perinatal factors studied, only the duration of stage 1 labor was found to be associated with significant elevations in the leukocyte and absolute neutrophil counts. Conclusions: Previously published normal ranges for leukocyte indexes in healthy newborn infants during the early neonatal period are too restrictive; reference standards should be broadened. (J PEDIATR 1994;125:603-6).