Polycythemia in the newborn.

Polycythemia is defined as a venous hematocrit above 65%. The relationship between viscosity and hematocrit is almost linear till 65% and exponential thereafter. Increased viscosity of blood is associated with symptoms of hypo-perfusion. The hematocrit in a newborn peaks at 2 hours of age and decreases gradually after that. The etiology of polycythemia is related either to intra-uterine hypoxia or secondary to fetal transfusion. Clinical features related to hyperviscosity may affect all organ systems and this entity should be screened for in high-risk infants. Polycythemia maybe symptomatic or asymptomatic and guidelines for management of both types are provided in the protocol.