Polycythemia and hyperviscosity of the newborn.

Polycythemia and hyperviscosity of the newborn are well-known conditions that are surrounded by controversy. The patient population most affected by polycythemia is the term or near-term infant. The true incidence of this condition is not known since the majority of infants are likely to be asymptomatic, normal newborns. Diagnosis is largely based on hematocrit values and symptoms, which can range from subtle to severe, and not on measures of viscosity. Hematocrits are not routinely drawn in this population, most likely related to the controversy surrounding the treatment of the asymptomatic infant. Presenting symptoms may be subtle and are not always attributed to polycythemia. Knowledge of the etiology, pathophysiology, and clinical signs and symptoms may contribute to the early identification and treatment of infants with polycythemia and hyperviscosity syndrome.