The immature platelet fraction: creating neonatal reference intervals and using these to categorize neonatal thrombocytopenias

OBJECTIVE: The immature platelet fraction (IPF) is a laboratory measurement analogous to the reticulocyte count, but reflecting the thrombopoietic state. Similar to a reticulocyte count, it can be expressed as a percent (IPF% = percent of platelets that are immature) or as an absolute number per mu l blood; the immature platelet count (IPC=IPF% x platelets per mu l of blood). STUDY DESIGN: Using a retrospective analysis of de-identified data from non-thrombocytopenic neonates, we created reference intervals for IPF% and IPC. We then tested the value of these measurements for categorizing thrombocytopenic neonates. RESULTS: New charts display reference intervals for IPF% and IPC on the day of birth according to gestational age, and during the first 90 days after birth. Neonates with hyporegenerative varieties of thrombocytopenias (syndromes, small for gestational age, birth asphyxia) had lower IPF% and IPC than did neonates with consumptive thrombocytopenias (immune-mediated, infection, disseminated intravascular coagulation, necrotizing enterocolitis; both P < 0.0001). CONCLUSION: The new reference interval charts can be used to recognize abnormal IPFs. The IPF parameters can help clarify the kinetic mechanism responsible for thrombocytopenias in neonates.