Intracellular neutrophil myeloperoxidase level in pediatric patients: Significant age and gender variability

Introduction: Myeloperoxidase (MPO) is an enzyme produced by neutrophil leukocytes and released upon activation, killing pathogens and causing tissue damage. As neutrophils in neonates are functionally immature, cellular MPO content in children may be age-related and different from adults. Hematological analyzer ADVIA 2120i (Siemens AG), while routinely assessing neutrophil count, measures their MPO content by means of myeloperoxidase index (MPXI). No pediatric reference range for MPXI has been published. Methods: We performed a retrospective study of MPXI values in 51 303 consecutive routine blood tests of nonhematologic pediatric patients, looking for age- and gender-related variability. Nonparametric statistical analysis (Spearman rho and Mann-Whitney U-test) was used for evaluation. Results: Neutrophil MPO content was highly significantly lower during the first month of life (P << 0.001) and rose to average pediatric values by day 28. Unexpectedly, the study revealed a highly significant gender difference (P << 0.001), MPXI being lower in boys from birth to adulthood. Conclusions: We found previously unreported highly significant age- and gender-related variations of neutrophil MPO in children in hospital setting. There are possible clinical implications, particularly concerning neutrophil immunity of neonates and gender-related difference in vascular events in adults. The finding may be considered for refining automatic cell counting in infants.