What is Polycythemia Vera?

By  ,  National Institute of Health
Jan 09, 2013

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Polycythemia (POL-e-si-THE-me-ah) vera (VAY-rah or VE-rah), or PV, is a rare blood disease in which your body makes too many red blood cells.

The extra red blood cells make your blood thicker than normal. As a result, blood clots can form more easily and block blood flow through your arteries and veins. This can lead to heart attack and stroke.

Thicker blood also flows more slowly to all parts of your body, preventing your organs from getting enough oxygen. This can cause other serious complications, such as angina (an-JI-nuh or AN-juh-nuh) and heart failure.


Red blood cells carry oxygen to all parts of your body. They also remove carbon dioxide (a waste product) from your body's cells and carry it to the lungs to be exhaled.

Red blood cells are made in your bone marrow-a sponge-like tissue inside the bones. White blood cells and platelets (PLATE-lets) also are made in your bone marrow. White blood cells help fight infection. Platelets help your blood clot.

If you have PV, your bone marrow makes too many red blood cells. It also can make too many white blood cells and platelets.

A mutation, or change, in the body's JAK2 gene is the major cause of PV. The JAK2 gene makes an important protein that helps the body produce blood cells. What causes the change in the JAK2 gene isn't known. PV generally isn't passed from parent to child.
PV develops slowly and may not cause symptoms for years. Thus, the disease often is found during routine blood tests done for other reasons.

When signs and symptoms do occur, they're the result of the thick blood that occurs with PV. This thickness slows the flow of oxygen-rich blood to all parts of your body. Without enough oxygen, many parts of your body won't work normally.

For example, slower blood flow deprives your arms, legs, lungs, and eyes of the oxygen they need. This can cause headaches, dizziness, itching, and vision problems, such as blurred or double vision.


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