Saturday, June 15, 2024

Polycythemia of the Newborn

Background

The term polycythemia means an increased cell number. However, it is mostly used to refer specifically to increased circulating red blood cell (RBC) mass. RBC mass is estimated using the hematocrit (Hct) measurement, which is defined as the percentage of RBCs in a given volume of blood. Term newborns usually have a higher Hct (51 ± 7%) compared to older children and adults. This increased Hct is a normal compensatory mechanism in these infants for the relative tissue-level hypoxia that is prevalent in the intrauterine environment, and it is exacerbated by the high affinity of fetal hemoglobin for oxygen.
 Polycythemia in the newborn is defined as a central venous Hct over 65% or a hemoglobin value above 22 g/dL.

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