Objectives: We previously described a severe, prolonged, idiopathic, but self-resolving, variety of neutropenia among preterm neonates. In the present study, we sought to assess the marrow neutrophil reserves of these patients by serially measuring blood neutrophils following the administration of recombinant granulocyte colony-stimulating factor (rG-CSF) or placebo.
Study design: Prospective, randomized trial of rG-CSF vs placebo for infants with "idiopathic neonatal neutropenia".
Results: During 36 consecutive months, 2407 neonates were admitted to the neonatal intensive care unit; 429 weighed less than 1500 g at birth, 14 of these were later diagnosed with "idiopathic neonatal neutropenia"; 10 were enrolled in this trial. The five rG-CSF recipients had an immediate, marked increase in blood neutrophil concentration, indicating adequate rG-CSF-mobilizable marrow neutrophil reserves. This effect persisted to day 5, but counts were not different from those of the five placebo recipients on days 12 and 15.
Conclusions: Patients with "idiopathic neonatal neutropenia" have a substantial rG-CSF-mobilizable marrow neutrophil reserve. On that basis, we speculate that this variety of neonatal neutropenia does not constitute a significant deficiency in antibacterial defense.