Platelet function in the newborn

Whole blood flow cytometry, an important new method for the assessment of platelet function, is particularly advantageous for neonatal studies because only minuscule volumes (similar to 2 mu L) of blood are required. By this method, we have demonstrated that neonatal platelets are less reactive than adult platelets to physiological agonists in whole blood, as determined by the activation-induced increase in the platelet surface expression of P-selectin and the glycoprotein (GP) IIb-IIla complex and by the activation-induced decrease in the platelet surface expression of the GPIb-IX complex. Our data suggest that the mechanism of neonatal platelet hyporeactivity is, at least in part, a relative defect in a common signal transduction pathway. We have further demonstrated that the platelets of very low birth weight (VLBW) preterm neonates are maximally hyporeactive on days 3 to 4 of life but return to almost the adult range by days 10 to 14, Given that intraventricular hemorrhage (IVH) is also maximal on days 3 to 4, these defects may contribute to the propensity of VLBW preterm neonates to IVH.