• What Happens When the Body Makes Too Many Red Blood Cells?

Blood Disorder Causes Body to Make Too Many Red Blood Cells

April 8, 2011

Dear Mayo Clinic:

What is the latest research and treatment for polycythemia vera?


Polycythemia vera (PV) is a blood disorder in which the body makes too many red blood cells. It's one in a family of diseases called myeloproliferative disorders. In these diseases, bone marrow — the spongy tissue inside bones where blood cells are made — is affected by a type of chronic leukemia that causes it to make more cells than it should. In PV, too many red blood cells are produced, but sometimes it can also result in too many white blood cells or too many platelets (the component of blood that aids in clotting). A considerable amount of research is currently investigating PV and its treatment.

Exactly why PV develops is still unclear. But researchers know more about the cause of the disease now than in the past. In 2005, researchers found that a change (mutation) in a gene that affects the protein JAK2 appears to play a role in PV development. JAK2 is one in a series of on/off switches that control when cells grow and divide. In PV, this on/off switch is stuck in the on position, causing cell growth to continue. About 95 percent of people with PV have the JAK2 mutation, but others have different mutations that may affect cells in a similar way. Researchers are currently investigating those mutations to learn more.

In its early stages, PV may not cause symptoms. Due to the excess red blood cells, though, some people may eventually develop skin itchiness and redness, headaches, dizziness, shortness of breath, and numbness, tingling, burning or weakness in their hands, feet, arms or legs. Because PV causes blood to thicken and slow, it can also increase the risk of developing blood clots, which can cause a stroke.

Over the long term, PV may progress to myelofibrosis, a disorder that involves scarring in the bone marrow, disruption of the production of blood cells, and can lead to enlargement of the spleen and liver. PV can also progress to acute leukemia, a cancer of the blood and bone marrow.

Treatment of PV focuses on controlling symptoms and decreasing the risk of blood clots or bleeding. Therapies often include a daily dose of aspirin and reducing the amount of red blood cells by periodically drawing blood from a vein (phlebotomy).

In some high-risk patients, medication may be used to decrease the number of red blood cells or to suppress the bone marrow's ability to produce blood cells. People who require medication for PV typically include those older than 60; individuals who have previously had blood clots or bleeding; people who are at high risk of heart disease; and those with significantly elevated platelet counts. Currently, two main drugs are available to treat PV. The first is hydroxyurea, which can lower the amount of red blood cells, white blood cells and platelets. The second is anagrelide, which lowers only the amount of platelets.

A variety of other PV medications are under investigation. Recent research has shown that a long-acting form of the drug interferon, called pegylated interferon 2 alpha, may be a promising new drug for PV treatment. This drug can help lower blood cell counts, but recent studies suggest it may also lower the levels of the abnormal JAK2 protein in blood. Several large clinical research trials are exploring the role of this drug in treating people who have high-risk PV. Other research studies are examining a class of drugs known as JAK2 inhibitors. Researchers believe these drugs may work to treat PV by blocking the effect of the defective JAK2.

Overall, the future is bright for people with PV. Much more is known about this disease now than just a few years ago. Many avenues of investigation into new treatments are under way. The hope is that these therapies will not only help people with this disease feel better in the short term, but also make PV a more manageable disease in the long term.

— Ruben Mesa, M.D., Hematology, Mayo Clinic, Scottsdale, Ariz.

Related articles