title: 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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Division of Neonatology, Department of Pediatrics, Hospital Universitari Son Espases, Palma de Mallorca, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Vetter-Laracy
authors.affiliation: Division of Neonatology, Department of Pediatrics, Hospital Universitari Son Espases, Palma de Mallorca, Spain.
authors.forename: P-R
authors.initials: PR
authors.lastname: Balliu
authors.affiliation: Division of Hematology-Oncology, Department of Pediatrics, Hospital Universitari Son Espases, Palma de Mallorca, Spain.
authors.forename: J A
authors.initials: JA
authors.lastname: Salinas
authors.affiliation: Department of Hematology, Hospital Universitari Son Espases, Palma de Mallorca, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Duran
mesh_terms: D017668:Age of Onset; D002543:Cerebral Hemorrhage / Q000150:complications; D004921:Erythropoietin / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D007234:Infant, Premature; D007235:Infant, Premature, Diseases / Q000097:blood / Q000453:epidemiology; D019102:Infant, Very Low Birth Weight / Q000097:blood*; D007958:Leukocyte Count; D008297:Male; D009503:Neutropenia / Q000097:blood* / Q000188:drug therapy / Q000453:epidemiology; D012189:Retrospective Studies
chemical_list: D004921:Erythropoietin
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