Polycythemia vera (POL-e-si-THEE-me-ah 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. These clots can block blood flow through your arteries and veins, which can cause a heart attack or stroke.
Thicker blood also doesn't flow as quickly to your body as normal blood. Slowed blood flow prevents your organs from getting enough oxygen, which can cause serious problems, such as angina (an-JI-nuh or AN-juh-nuh) and heart failure. (Angina is chest pain or discomfort.)
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 stick together to seal small cuts or breaks on blood vessel walls and stop bleeding.
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. This gene makes a protein that helps the body produce blood cells. What causes the change in the JAK2 gene isn't known. PV generally isn't inherited—that is, passed from parents to children through genes.
PV develops slowly and may not cause symptoms for years. The disease often is found during routine blood tests done for other reasons.
When signs and symptoms are present, 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.
PV is a serious, chronic (ongoing) disease that can be fatal if not diagnosed and treated. PV has no cure, but treatments can help control the disease and its complications.
PV is treated with procedures, medicines, and other methods. You may need one or more treatments to manage the disease.