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Neonatal polycythemia

Joseph A Garcia-Prats, MD
Section Editors
Donald H Mahoney, Jr, MD
Leonard E Weisman, MD
Deputy Editor
Carrie Armsby, MD, MPH


Neonatal polycythemia is characterized by a venous hematocrit (hct) that greatly exceeds normal values for gestational and postnatal age. This condition affects approximately 1 to 5 percent of newborns. Although many affected infants are asymptomatic, the characteristic clinical features are thought to result from hyperviscosity and/or the metabolic effects of an increased red blood cell mass.


Normal newborn physiology — Compared with older infants and children, term newborns have an increased red cell mass caused by the fetal response of increased hemoglobin production to a relatively hypoxic intrauterine environment and possibly vasomotor instability and venous pooling in newborn immediately after birth. The mean hematocrit (hct) and hemoglobin concentrations from capillary samples in healthy term infants at birth are 61±7 standard deviations (SD) percent and 19.3±2.2 (SD) g/dL, respectively [1].

Polycythemia — Polycythemia is defined as hct or hemoglobin concentration >2 SD above the normal value for gestational and postnatal age [2]. Accordingly, a term infant is considered to be polycythemic if the hct from a peripheral venous sample is >65 percent or the hemoglobin is >22 g/dL [3-6]. In clinical circumstances, the definition typically is based upon the hct, rather than the hemoglobin concentration.

The diagnosis of polycythemia is based upon peripheral venous samples because of the variability in measurements obtained from capillary samples. Hcts of blood from venous samples may be as much as 15 percent lower than those obtained from capillary samples. (See 'Laboratory testing' below.)

Hyperviscosity — Polycythemia must be distinguished from hyperviscosity, which is defined as a blood viscosity >12 centipoise, measured at a shear rate of 11.5 per second; or >6 centipoise, measured at a shear rate of 106 per second [7]. Whole blood viscosity can be affected by significant increases in any of the elements of whole blood including red cells, white cells, platelets, plasma proteins, immunoglobulins or clotting factors. In neonates, the focus is generally on red cell excess [8].

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Literature review current through: Nov 2017. | This topic last updated: Sep 19, 2016.
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