Secondary polycythemia is the overproduction of red blood cells. It causes your blood to thicken, which increases the risk of a stroke. It’s a rare condition.

The primary function of your red blood cells is to carry oxygen from your lungs to all the cells in your body.

Red blood cells are constantly being manufactured in your bone marrow. If you move to a higher altitude where oxygen is rarer, your body will sense this and begin to produce more red blood cells after a few weeks.

Secondary vs. primary

Secondary polycythemia means that some other condition is causing your body to produce too many red blood cells.

Usually you’ll have an excess of the hormone erythropoietin (EPO) that drives the production of red cells.

The cause could be:

  • a breathing obstruction such as sleep apnea
  • lung or heart disease
  • use of performance-enhancement drugs

Primary polycythemia is genetic. It’s most commonly caused by a mutation in the bone marrow cells, which produce your red blood cells.

Secondary polycythemia can also have a genetic cause. But it’s not from a mutation in your bone marrow cells.

In secondary polycythemia, your EPO level will be high and you’ll have a high red blood cell count. In primary polycythemia, your red blood cell count will be high, but you’ll have a low level of EPO.

Technical name

Secondary polycythemia is now technically known as secondary erythrocytosis.

Polycythemia refers to all the types of blood cells — red cells, white cells, and platelets. Erythrocytes are the red cells only, making erythrocytosis the accepted technical name for this condition.

The most common causes of secondary polycythemia are:

Other common causes of secondary polycythemia include:

Finally, some diseases can cause your body to overproduce the hormone EPO, which stimulates red blood cell production. Some of the conditions that can cause this are:

  • certain brain tumors (cerebellar hemangioblastoma, meningioma)
  • tumor of the parathyroid gland
  • hepatocellular (liver) cancer
  • renal cell (kidney) cancer
  • adrenal gland tumor
  • benign fibroids in the uterus

In rare cases, the cause of secondary polycythemia can be genetic. This is usually due to mutations that cause your red blood cells to take up abnormal amounts of oxygen.

The risk factors for secondary polycythemia (erythrocytosis) are:

  • obesity
  • alcohol abuse
  • smoking
  • high blood pressure (hypertension)

A recently discovered risk is having a high red cell distribution width (RDW), which means that the size of your red blood cells can vary a lot. This is also known as anisocytosis.

Symptoms of secondary polycythemia include:

  • breathing difficulty
  • chest and abdominal pain
  • fatigue
  • weakness and muscle pain
  • headache
  • ringing in ears (tinnitus)
  • blurred vision
  • burning or “pins and needles” sensation in hands, arms, legs, or feet
  • mental sluggishness

Your doctor will want to determine both secondary polycythemia and its underlying cause. Your treatment will depend on the underlying cause.

The doctor will take a medical history, ask you about your symptoms, and physically examine you. They’ll order imaging tests and blood tests.

One of the secondary polycythemia indications is a hematocrit test. This is part of a complete blood panel. Hematocrit is a measure of the concentration of red blood cells in your blood.

If your hematocrit is high and you also have high EPO levels, it could be a sign of secondary polycythemia.

The main treatments for secondary polycythemia are:

  • low-dose aspirin to thin your blood
  • bloodletting, also known as phlebotomy or venesection

Low-dose aspirin works as a blood thinner and can reduce your risk of stroke (thrombosis) from the overproduction of red blood cells.

Drawing up to a pint of blood reduces the concentration of red cells in your blood.

Your doctor will determine how much blood should be drawn and how often. The procedure is almost painless and has a low risk. You need to rest after a blood draw and be sure to have a snack and plenty of liquids afterward.

Your doctor may also prescribe some medications for relief of your symptoms.

When not to lower red blood cell count

In some cases, your doctor will choose not to lower your elevated red blood cell count. For example, if your raised count is a reaction to smoking, carbon monoxide exposure, or a heart or lung disease, you may need the extra red blood cells to get enough oxygen to your body.

Long-term oxygen therapy can then be an option. When more oxygen gets to the lungs, your body compensates by producing fewer red blood cells. This reduces blood thickness and the risk of stroke. Your doctor may refer you to a pulmonologist for oxygen therapy.

Secondary polycythemia (erythrocytosis) is a rare condition that causes your blood to thicken and increases the risk of stroke.

It’s usually due to an underlying condition, which can range in severity from sleep apnea to serious heart disease. If the underlying condition isn’t serious, most people with secondary polycythemia can expect a normal lifespan.

But if the polycythemia makes the blood extremely viscous, there’s an increased risk of stroke.

Secondary polycythemia doesn’t always require treatment. When needed, treatment is usually low-dose aspirin or blood drawing (phlebotomy).