Anemia of Prematurity - Portal Neonatal

Polycythemia of the Newborn
Last Updated: June 3, 2005
Synonyms and related keywords: neonatal polycythemia, erythrocythemia, hematocrit, Hct,
hyperviscosity, sludged blood, microthrombi, microthrombus
AUTHOR INFORMATION Section 1 of 9
Author: Karen J Lessaris, MD, Attending Staff, Department of Neonatology, Carolinas Medical
Center
Karen J Lessaris, MD, is a member of the following medical societies: American Academy of
Pediatrics
Editor(s): Scott MacGilvray, MD, Associate Professor, Department of Pediatrics, Pitt County
Memorial Hospital; Robert Konop, PharmD, Director, Clinical Account Management, Ancillary
Care Management; Brian S Carter, MD, Associate Director, Associate Professor, Department of
Pediatrics, Division of Neonatology, Vanderbilt University Medical Center and Gateway Medical
Center; Carol L Wagner, MD, Associate Professor, Department of Pediatrics, Division of
Neonatology, Medical University of South Carolina; and Neil N Finer, MD, Director, Division of
Neonatology, Professor, Department of Pediatrics, University of California at San Diego
INTRODUCTION Section 2 of 9
Background: Polycythemia, defined as a venous hematocrit (Hct) of greater than 65%, is a
relatively common disorder. The primary concern with polycythemia is related to hyperviscosity and
its associated complications. Blood viscosity increases exponentially as the Hct rises above 42%.
This associated hyperviscosity is thought to contribute to the symptom complex observed in
approximately one half of infants with polycythemia. However, only 47% of infants with polycythemia
have hyperviscosity, and only 24% of infants with hyperviscosity have a diagnosis of polycythemia.
Pathophysiology: As the central Hct increases, viscosity increases, resulting in abnormal blood flow
kinetics. This condition manifests as poor flow or sludging of blood, which predisposes the infant to
microthrombi and decreased tissue oxygenation. Many factors determine blood viscosity. As
previously mentioned, viscosity increases as Hct rises. Plasma volume, plasma proteins, platelets,
and endothelial factors also contribute to viscosity. Factors unique to the neonate (eg, increased
RBC volume, decreased deformability of the fetal erythrocyte) also contribute to increased viscosity.
Frequency: In the US: Polycythemia occurs in 0.4-12% of neonates. It is more common in infants
who are small for their gestational age (SGA) and in infants who are large for their gestational age
(LGA). However, most infants with polycythemia are of appropriate size or weight for their gestational
age (AGA). Infants of mothers with diabetes have an incidence of >40%, and those born to mothers
with gestational diabetes have an incidence of >30%. Hyperviscosity occurs in 6.7% of infants.
Mortality/Morbidity:
Age:
• The central nervous, cardiopulmonary, gastrointestinal, and renal systems are at risk.
• Metabolic derangements are common.
• Coagulation also can be affected.
• The Hct peaks 2 hours after birth and then declines until the infant is aged 6 hours, at which
time it equals the Hct in cord blood.
• Fewer than 40% of infants with a Hct greater than 64% at 2 hours still have a high value at
12 hours or later.