Late-onset neutropenia: defining limits of neutrophil count in very low birth weight infants

Abstract

Objective: To evaluate the incidence, onset, duration, characteristics and importance of late-onset neutropenia (defined as absolute neutrophil count<1500 μl(-1) at 3 weeks of age or later) in a group of very low birth weight (VLBW) infants.

Study design: Routine complete blood cell counts (CBCs) obtained from VLBW infants over a period of 7 years were gathered retrospectively, including those of newborns with weekly CBCs taken over a duration of at least 3 weeks. Data were obtained from between January 2003 and December 2009.

Result: CBCs of 399 newborns were included. Values were obtained from birth to 36 weeks of postnatal age. Late-onset neutropenia was observed in 259 cases (65%). Neutropenic infants had a mean of 0.5 weeks lower gestational age. Late-onset neutropenia was more frequent in children with intraventricular hemorrhage but not in patients who received erythropoietin. The median age of neutropenia onset was 7 weeks in extremely low birth weight infants and 6 weeks in VLBW infants. The fifth percentile of neutrophils between weeks 3 and 4 was 1280 μl(-1) and between weeks 13 and 15 was 500 μl(-1). The average duration was 2 weeks with normalized values after 18 weeks.

Conclusion: A neutrophil count <1500 μl(-1) after the third week of life is frequently observed in VLBW infants and should not be used as a lower reference limit. The fifth percentile varies according to postnatal age from around 1300 μl(-1) in week 4 of life, decreasing to a nadir of 500 μl(-1) between 3 and 4 months of age. Values normalize in the first year of life.