FLOW-CYTOMETRY OF NEONATAL PLATELET RNA

Purpose: Serious disorders of hemostasis occur more often in the small , stressed preterm infant, partly due to immaturity of the newborn hem ostatic mechanism. Information regarding the maturational development of platelets in infants has been limited by the large amounts of blood historically needed for platelet studies. The objective of this study was to determine differences between platelets in adults and infants by flow cytometric analysis of ''reticulated'' platelets. Patients and Methods: Eighteen normal adults, 42 healthy term infants, and 27 pret erm infants were studied. The infants were subdivided by mode of deliv ery: vaginal or Caesarean section. Platelet-rich plasma from adult who le blood and infant cord blood samples was divided into aliquots conta ining 5 x 10(6) platelets, fixed with 1% paraformaldehyde, and stained with thiazole orange for RNA content. The percentage of RNA positive ''reticulated'' platelets in each aliquot was then determined by flow cytometry. Results: Group comparisons using ANOVA statistical analysis showed a significant difference (p < 0.05) for platelet RNA content b etween adults and term infants, the adults having a higher percentage of reticulated platelets. Although the difference was smaller, adults also had a higher percentage of reticulated platelets than preterm inf ants. There was no significant difference in reticulated platelet valu es between infants within one gestational age group compared by type o f delivery. Conclusion: There are demonstratable differences in adult and infant platelet RNA content that may reflect developmental differe nces in megakaryocytic/platelet kinetics.