Background: Reticulated platelets (RPs) are newly synthesized platelets. Recently, an automatic method was established to detect RPs as a percentage of the immature platelet fraction (IPF%). Although, neonates often develop thrombocytopenia at some time during their hospitalization, the details of IPF% in neonates remain unclear. We, therefore, studied the relations between IPF% and other factors to gain a more detailed understanding of IPF% in neonates. Methods: The following clinical data were obtained from the medical records of 105 neonates who met our inclusion criteria: Gestational age, birth weight, IPF% and platelet count of neonatal peripheral blood at birth, and perinatal data. The subjects were divided into three groups: Group A, birth weight standard deviation score (SDS) ≥ −2 standard deviation (SD) and ≤ +2 SD; Group S, < −2 SD; and Group L, > +2 SD. Results: IPF% correlated negatively with platelet count at birth in the whole study population. IPF% was 2.8 ± 1.3% in term neonates, and IPF correlated negatively with gestational age and birth weight. Platelet count correlated positively with birth weight SDS in the whole study population and in Group S. IPF% correlated negatively with birth weight SDS in the whole study population and in Group S. In neonates with a platelet count below 25 × 104/μl, IPF% correlated negatively with platelet count. Among other neonates, however, IPF% remained almost constant. Conclusion: Monitoring of IPF% is useful for estimating the function of thrombocytopoiesis in neonates and preterm infants.
