Flow cytometry of neonatal platelet RNA

Serious disorders of hemostasis occur more often in the small, stressed preterm infant, partly due to immaturity of the newborn hemostatic 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.

Eighteen normal adults, 42 healthy term infants, and 27 preterm infants were studied. The infants were subdivided by mode of delivery: vaginal or Caesarean section. Platelet-rich plasma from adult whole blood and infant cord blood samples was divided into aliquots containing 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.

Group comparisons using ANOVA statistical analysis showed a significant difference (p<0.05) for platelet RNA content between 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 infants. There was no significant difference in reticulated platelet values between infants within one gestational age group compared by type of delivery.

There are demonstratable differences in adult and infant platelet RNA content that may reflect developmental differences in megakaryocytic/platelet kinetics.