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

Hyperviscosity can occur when the percentage of red blood cells (RBCs) in the infant's blood is greater than 65%. This may result from various conditions that develop before birth, such as:

• Birth defects
• Delay in clamping the umbilical cord
• Inherited diseases
• Not enough oxygen reaching body tissues (hypoxia)

The extra RBCs block the flow of blood in the smallest blood vessels. This leads 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
• Very ruddy (red) skin color

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, a substance produced by muscles that can build up in the blood if the kidneys aren't working properly
• Urinalysis