Hyperviscosity

Alternative names:

hyperviscosity of the newborn; neonatal polycythemia

Definition:

Hyperviscosity in the newborn is defined as increased resistance to blood flow as a result of an abnormally high hematocrit (percentage of red blood cells in the whole blood) level.

Causes, incidence, and risk factors:

Hyperviscosity results when the percentage of red blood cells (RBCs) in the infant's blood is greater than 65%. High hematocrits may result from various intrauterine conditions such as hypoxia, inherited diseases, and congenital abnormalities.

The high percentage of RBCs causes blockage of blood flow in the smallest capillaries. This leads to tissue death from lack of oxygen. This blocked blood flow can affect all organs such as the kidneys, lungs, and brain.

Infants with hyperviscosity may develop feeding problems, cyanosis, low blood sugar, elevated bilirubin (jaundice), and other more ominous findings. Central nervous system damage may appear later as learning disabilities, speech problems, and other subtle defects.