Developmental hemostasis: Primary hemostasis and evaluation of platelet function in neonates

Hemostasis is a dynamic process and physiologic concentrations of coagulation proteins gradually increase with gestational age. Nevertheless, the risk for bleeding in term neonates is counterbalanced by the protective effects of physiologic deficiencies of the inhibitors of coagulation. Although laboratory diagnosis of coagulation disorders in infants may be difficult to establish, due to the need to adapt all assays for small amounts of blood and the age-related interpretation required for test results - evaluation of infants with secondary hemostatic defects is quite feasible, whereas laboratory assessment of primary hemostasis in neonates remains a challenge. While platelet number and volume are similar in neonates as compared to adult values, neonatal platelets certainly exhibit hyporesponsiveness. Analysis of platelet function may include aggregation studies or flow cytometry assays, using fluorescence-stained monoclonal antibodies against platelet membranes and cellular antigens. Data on platelet function in correlation with gestational age are scarce and the duration of platelet hyporeactivity and its clinical significance have not yet been completely elucidated. Whole-blood-based platelet function assays have shown in neonates as well as in premature infants progressive improvement of clot formation with gestational age. This article reviews platelet function, assessed by various techniques, and its development in the premature as well as healthy term neonate.