Neonatal platelets are less reactive than adult platelets to physiological agonists in whole blood.

Previous studies have reported that the platelets of healthy term neonates have either diminished or normal reactivity compared to the platelets of adults. To circumvent the methodologic problems of previous studies, we used a whole blood flow cytometric method to study neonatal platelet reactivity to thrombin, a combination of ADP and epinephrine, and U46619 (a stable thromboxane A 2 analogue). Inclusion in the assay of the peptide GPRP (an inhibitor of fibrin polymerization) enabled us to study platelet reactivity to human α-thrombin in whole blood. Umbilical cord blood and day 1 peripheral blood were collected from 30 healthy term neonates and compared to peripheral blood from 20 normal adults