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Polycythaemia vera (PV)

This page is about polycythaemia vera (PV). There is information about


What PV is

Polycythaemia vera (PV) is pronounced pol-ee-sigh-thee-me-a vee-rah. Poly means many and cythaemia relates to blood cells. It is also sometimes called erythrocytosis, which means too many red blood cells. And it used to be called polycythaemia rubra vera or PCRV.

PV is a type of rare blood disorder called a myeloproliferative neoplasm. These are conditions that cause an increase in the number of blood cells. We have a separate question and answer explaining myeloproliferative neoplasms.

Blood cells are made in the soft inner part of the bones, the bone marrow. All blood cells start from the same type of cell called a blood stem cell. The stem cell makes immature blood cells. The immature cells go through various stages of development before they become fully developed blood cells and are released into the blood as

  • Red blood cells to carry oxygen
  • White blood cells to fight infection
  • Platelets to help the blood clot

The diagram shows how the various different types of cells develop from a single blood stem cell.


In polycythaemia vera, the stem cells make too many red blood cells. This makes the blood become thicker. Sometimes the extra cells collect in the spleen, which may then become enlarged.

For most people, treatment controls PV for many years. But for some people PV can lead to other problems. Just under a third of people (30%) develop scarring of their bone marrow, which is called myelofibrosis. And about 1 in 20 people (5%) develop acute myeloid leukaemia.

PV can develop without having had any other condition. This is called primary polycythaemia vera. It is caused by a change in the control mechanism in cells. There is also another type called secondary polycythaemia. Secondary polycythaemia is caused by having low levels of oxygen over a long period of time. This usually happens if you have heart or lung disease. But it can develop if you smoke or work in a poorly ventilated area.


Risks and causes

We know from research that more than 9 out of 10 people who have polycytheamia vera have a change in the JAK2 gene. The JAK2 gene makes a protein that controls how many blood cells the stem cells make. We need more research to find out what causes the change in the JAK2 gene.

Some research suggests that exposure to the chemical benzene may increase your risk of developing polycythaemia vera. You are most likely to come into contact with benzene through work. It is used in the rubber industry and is one of the chemicals in petrol. Exposure to radiation may also slightly increase your risk.



Many people find out they have PV when they are having a blood test for something else. This is because PV usually develops slowly and doesn’t cause symptoms at first. As the condition progresses it causes symptoms. These include

  • Headaches
  • Feeling breathless
  • Blurred vision
  • Night sweats
  • Reddening of the skin
  • Itching
  • Left sided swelling or pain from an enlarged spleen
  • Higher blood pressure than normal
  • Gout
  • Bleeding or blood clots, which can sometimes lead to stroke or heart problems

Polycythaemia is rare so if you have any of these symptoms it is more likely to be something else. But it is still important to contact your doctor to find out what is causing them.


Blood tests and other tests

The first test to diagnose PV is a blood test. This is to check

The haematocrit level is the amount of space the red blood cells take up in the blood. When there are more blood cells they take up more space and so the haematocrit level is higher.

Around half of those with PV (50%) have an increase in the number of platelets.

If your first blood test suggests you have PV, you may have a blood test to look for a change in a gene called JAK2.

Other tests you may have include

  • A bone marrow test
  • Chest X-ray
  • Blood test to measure your level of a blood cell growth factor called EPO
  • Ultrasound scan to check the size of your spleen
  • Blood tests to check how well your liver and kidneys are working
  • A test to measure the oxygen level in your blood (pulse oximetry)

The outlook for PV

Polycythaemia vera usually develops very slowly. Many patients live with the disease for decades.



Treatment for PV aims to reduce the number of red blood cells. This helps to control your symptoms and to prevent any more serious problems. The treatment you need will depend on your risk of more serious problems, such as blood clots. Treatments include

Having blood taken

Your doctor may call this venesection but it only means taking blood. For PV, you will have about a pint of blood removed. After this treatment, you will have fewer red blood cells. You can have this treatment repeated.

Low dose aspirin

Around half of those with PV have a high number of platelets in their blood, as well as a high red cell count. This can cause problems with blood clots. Low dose aspirin can lower your risk of getting a blood clot. You take it as a tablet.


You may have chemotherapy if venesection isn’t working and your spleen is enlarged and causing symptoms.

This treatment uses cell killing (cytotoxic) drugs to destroy the immature blood cells. The drugs work by disrupting the growth of cells and stopping them from dividing. It helps to lower the number of red blood cells and platelets. There is a small increase in the risk of developing a leukaemia if you have this treatment repeatedly over a long time. You may have the following chemotherapy drugs for PV

The links above will take you to more information about each drug and its side effects.


When red blood cells are broken down by the body they produce uric acid. If you have too much uric acid in your blood, it can collect in the joints and cause painful swelling, called gout. Allopurinol lowers the amount of uric acid in the blood and so helps to reduce the symptoms of gout.


This is a type of biological therapy. It helps to boost the immune system. It can also help to control the number of red blood cells and the symptoms of PV, especially itching. Side effects of interferon include flu like symptoms and tiredness.

Radioactive phosphorus therapy

This is a type of radiotherapy that helps to stop the bone marrow producing too many red blood cells. You may have this if you have advanced PV. It is rarely used but if it is, it's usually in older people. This is because research suggests it may increase the risk of developing leukaemia. There is more information about radioactive phosphorus therapy in the radiotherapy section.



Polycythaemia vera is one of a group of conditions called myeloproliferative neoplasms or myeloproliferative disorders. Researchers are looking into how these conditions develop. Some of this research is suggesting that it may be better to group them depending on whether they are JAK2 positive or negative rather than whether they are PV, myelofibrosis or essential thrombocythaemia. We need more research to find out the best way to group them and what the best treatment is.

Researchers are looking into new types of treatment to stop the JAK2 gene signalling to the stem cell to make blood cells. These are called JAK2 inhibitors. This research is at an early stage, but looks promising. It will be sometime before we know how well JAK2 inhibitors work. We are waiting for the results of the RESPONSE trial which is looking into how a JAK2 inhibitor called INC424 works.

The RELIEF study is comparing a drug called ruxolitinib with hydroxycarbamide to see which is better at treating symptoms of PV. Ruxolitinib is a type of biological therapy called a cancer growth blocker. This trial has closed and we are waiting for the results.

An early trial is looking at a drug called givinostat for polycythaemia vera. Givinostat is a drug that blocks proteins (enzymes) in the body called histone deacetylases. Blocking these enzymes may stop cells growing and dividing. Drugs that block these enzymes are called HDAC inhibitors. Researchers want to find out the best dose of givinostat to treat polycythaemia vera, how well it works, and what the side effects are.

You can search for polycythaemia vera trials in the UK on our clinical trials database


Coping with polycythaemia vera

Coping with a rare condition can be difficult both practically and emotionally. Being well informed about your condition and possible treatments can make it easier to make decisions and cope with what happens.

It can also help to talk to people with the same thing. But it can be hard to find someone with a rare condition. You can look at Cancer Chat – Cancer Research UK’s discussion forum. It is a place to share experiences, stories and information with other people who know what you are going through.

There are other organisations that also offer help and support.

MPD Voice
Website: www.mpdvoice.org.uk
They offer information and support to people with myeloproliferative disorders, including polycythaemia vera.

Leukaemia Care
Website: www.leukaemiacare.org.uk
They offer information and support to people with leukaemia and related blood conditions and have a message board.

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Updated: 25 February 2014