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Objectives
After completing this article, readers should be able to:
Define neutropenia for preterm and term neonates and the neutrophil concentrations that place infants at risk of developing infection.
List the most common causes of neonatal neutropenia.
Describe important factors in the evaluation of a neutropenic neonate.
Delineate the roles of recombinant granulocyte-colony-stimulating factor and granulocyte macrophage-colony-stimulating factor in the treatment of neonatal neutropenia.
Introduction
Neutropenia was described initially in 1902, but it was not reported as a problem in newborns until the late 1930s. (1)(2) Neutropenia now is recognized relatively commonly among ill neonates, affecting up to 8% of all patients in neonatal intensive care units (NICUs). (3)(4)(5)(6) Of the nearly 400,000 neonates admitted annually to NICUs in the United States, perhaps as many as 32,000 annually have neonatal neutropenia. The incidence of neonatal neutropenia is higher among preterm infants than among term infants, with estimates ranging between 6% and 58%, depending on the definition of neutropenia. (7) Often the neutropenia is transient and does not appear to convey a survival disadvantage. However, in some neonates, it is prolonged and severe, constituting a serious deficiency in antimicrobial defense. This article examines a general approach to the neutropenic neonate and some of the causes and treatments for this group of conditions.
Definition of Neutropenia
The diagnosis of neutropenia is based on a low blood neutrophil concentration. The blood neutrophil count can be calculated readily from a routine complete blood count as follows: 
The percent neutrophils generally is considered the sum of the segmented neutrophils, band neutrophils, and metamyelocytes.
Several investigators have provided normal expected ranges for blood neutrophil concentrations among neonates. The definition of neutropenia, the lower limit of normal for blood neutrophil concentrations, has been reported variously as 1,500/mcL, (8) 1,800/mcL, (9) and 1,100/mcL. (10) …
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