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Hyperviscosity - newborn


Hyperviscosity of the newborn is the slowing and blockage of blood flow. It occurs when there are too many red blood cells in an infant's blood.

Alternative Names

Neonatal polycythemia

Causes, incidence, and risk factors

Hyperviscosity can occur when the percentage of red blood cells (RBCs) in the infant's blood called the "hematocrit," is greater than 65%. The problem can occur as a result of conditions that develop before birth. These may include:

  • Birth defects
  • Delay in clamping the umbilical cord
  • Diabetes in the baby's birth mother
  • Inherited diseases
  • Not enough oxygen reaching body tissues (hypoxia)
  • Twin-twin transfusion syndrome (occurs when blood moves from one twin to the other)

The extra RBCs can block the flow of blood in the smallest blood vessels. This may lead to tissue death from lack of oxygen. This blocked blood flow can affect all organs, including the kidneys, lungs, and brain.


Symptoms may include:

  • Extreme sleepiness
  • Feeding problems
  • Seizures
  • Red skin color

Signs and tests

There may be signs of breathing problems, kidney failure, and newborn jaundice.

If the baby has symptoms of hyperviscosity, a blood test to count the number of red blood cells will be done. This test is called a hematocrit.

Other tests may include:

  • Blood gases to check oxygen level in the blood
  • Blood sugar (glucose) to check for low blood sugar
  • Blood urea nitrogen (BUN), a substance that forms when protein breaks down
  • Creatinine
  • Urinalysis


The baby will be monitored for complications of hyperviscosity. An exchange transfusion may be needed. This is done to lower the amount of red blood cells that are moving through the baby's blood vessels.

Other treatment may include increasing body fluids.

Expectations (prognosis)

The outlook is good for infants with mild hyperviscosity. Good results are also possible in infants who receive treatment for severe hyperviscosity.

Some children may have mild developmental changes. Parents should contact their health care provider if they think their child shows signs of delayed development.


Complications may include:

  • Death of intestinal tissue (necrotizing enterocolitis)
  • Decreased fine motor control
  • Kidney failure
  • Seizures
  • Strokes



Maheshwari A, Carlo WA. Blood disorders. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 97.

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