When a newborn has polycythemia, it means they have too many red blood cells. A doctor typically diagnoses polycythemia using a hematocrit test. Polycythemia can lead to thickening of the blood and potentially serious complications.

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Red blood cells (RBCs) carry oxygen from your lungs to the organs and tissues of your body. They also carry carbon dioxide, a waste gas, back to the lungs to be released when you exhale.

Polycythemia is a condition where there are too many RBCs in your body. When this occurs, it can cause the blood to become thickened and can lead to a variety of potentially serious complications.

Below, we’ll cover more about polycythemia in newborns, including its symptoms, what causes it, and how it’s diagnosed and treated. Continue reading to discover more.

Newborns with polycythemia have too many RBCs. Medically speaking, these newborns have a hematocrit value of over 65%.

Hematocrit is a measure of the percentage of your blood that’s made up of RBCs. So, for example, if your hematocrit value is 45%, that means that 45% of your blood is made up of RBCs.

Hematocrit values are typically higher in newborns than in adults. Levels peak in the hours after birth, then decline. Standard hematocrit values in newborns can range from 42–65%.

The high number of RBCs in polycythemia can cause the blood to thicken. This is referred to as hyperviscosity. Having hyperviscosity can mean that it’s more difficult for your body to deliver oxygen-rich blood to your organs and tissues.

Many newborns with polycythemia are asymptomatic, which means they do not have symptoms of the condition. It’s estimated that up to 47% of newborns who meet the criteria for polycythemia do have symptoms.

The signs and symptoms of polycythemia in newborns can include:

Newborns with polycythemia may also have atypical findings on several laboratory tests, including:

Several factors may cause the higher level of RBCs seen in newborn polycythemia, including:

Increases in RBCs can lead to hyperviscosity of the blood, reducing blood flow to vital organs and tissues. This is what leads to many of the symptoms of polycythemia, such as lethargy, rapid shallow breathing, and cyanosis.

If a newborn has symptoms like lethargy, breathing trouble, or cyanosis, a doctor can order tests to find out what’s causing these symptoms.

One of these tests will be a complete blood count (CBC). A CBC measures the levels of different blood cells and several other blood parameters, including hematocrit. A hematocrit higher than 65% indicates polycythemia.

Other tests that may be done include:

The optimal treatment for polycythemia in newborns is controversial. This is because there’s limited evidence that current treatment strategies improve outcomes.

Generally speaking, two types of treatment may be used for polycythemia in newborns. These are conservative treatment and partial exchange transfusion (PET).

Conservative treatment — or any treatment at all — for newborns with no symptoms of polycythemia is rarely advised, though a doctor may monitor their hematocrit and watch for any developing symptoms.

PET may be used for newborns with symptoms of polycythemia. This involves removing some of the newborn’s blood and replacing it with fluids from an IV line. This helps thin out the blood and reverse the effects of hyperviscosity.

Many newborns with polycythemia recover with no lasting effects. Newborns with severe hyperviscosity may experience complications, such as:

How common is polycythemia in newborns?

Polycythemia is estimated to affect 0.4–5% of healthy full-term newborns.

What factors put a newborn at risk of polycythemia?

Some of the factors that may increase a newborn’s risk of polycythemia include:

Is polycythemia in newborns life threatening?

In some cases, yes. Severe hyperviscosity can lead to potentially life threatening complications like necrotizing enterocolitis and stroke.

Polycythemia in newborns is when a newborn has too many RBCs. This is determined by measuring hematocrit levels.

Many newborns with polycythemia are asymptomatic. When symptoms are present, they can include lethargy, poor feeding, and rapid breathing.

It’s possible for polycythemia to lead to hyperviscosity, a thickening of the blood that can lead to potentially serious complications. Treatment for polycythemia in newborns may include fluids or PET.