What is polycythaemia vera (PV)?

Polycythaemia vera (PV) is a rare blood cancer that affects the bone marrow. It causes your body to make too many red blood cells. You pronounce it as pol-ee-sigh-thee-me-a vee-rah. Poly means many and cythaemia relates to blood cells. White blood cells and platelets are also often increased with this condition.

It is one of a group of conditions called myeloproliferative neoplasms (MPNs). MNPs are conditions that cause an increase in the number of blood cells.

The World Health Organisation (WHO) classes all myeloproliferative neoplasms as blood cancers. This is because the bone marrow is producing blood cells in an uncontrolled way. But many people with myeloproliferative neoplasms feel well and only need gentle treatment. The disorders often develop slowly and progress slowly. Or they can remain stable for a while.

Polycythaemia vera usually develops very slowly. It can affect people of any age. But it usually affects middle aged and older people. The average age at diagnosis is 60 years, but it can affect young adults. It can also affect children, although this is rare. Evidence suggests that it is slightly more common in men.

The bone marrow and blood cells

To understand more about PV, it helps to know how you make blood cells.

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 different types of cells develop from a single blood stem cell.

What happens in polycythaemia vera (PV)?

In polycythaemia vera, the stem cells make too many red blood cells. But white blood cells and platelets may also be affected.

Too many red blood cells can make the blood thicker. Having thicker blood makes it more difficult for your blood to flow around your body. It can also increase the risk of blood clots. Sometimes the extra cells are made in the spleen, which can make the spleen become enlarged.

If you have a higher number of platelets you may also be at risk of bleeding (haemorrhage).

For many people, treatment can control PV for many years. But for some people, PV can lead to other problems.

Over time PV can develop into myelofibrosis. This is scarring of their bone marrow. Less commonly, people with PV can develop acute myeloid leukaemia (AML).

Secondary polycythaemia

Having too many red blood cells in the blood is not always due to changes in the bone marrow. Lung disease and kidney disease can also lead to an increase in red blood cells. This is called secondary polycythaemia. Secondary polycythaemia can also develop if you smoke.

The treatment for secondary polycythaemia is different from PV. You will have treatment for the condition that caused the increase in blood cells. Your healthcare team will usually discuss how lifestyle changes could help.

Risks and causes

We know from research that more than 95 out of 100 people (more than 95%) who have polycythaemia vera have a change in the JAK2 gene. A fault in the JACK2 gene occurs in myeloproliferative neoplasms (MPNs).

The JAK2 gene makes a protein that controls how many blood cells the stem cells make. The fault with your JAK2 gene means the stem cells can start producing red blood cells when they're not meant to. This results in too many red cells being produced.

In most cases, these genetic faults happen during a person’s lifetime. You are not born with them, so you can’t pass them on to your children.

Family history

In rarer cases, you might have a history of myeloproliferative neoplasms in your family. This might mean there is a faulty gene in your family that increases your risk of developing MPNs.

Symptoms of polycythaemia vera (PV)

Many people find out they have PV when they are having a blood test for something else. Or you might find out you have PV after tests for another condition such as a blood clot. 

This is because PV develops slowly and doesn’t cause symptoms at first. As it progresses it causes symptoms. These include:

• headaches
• tiredness (fatigue)
• burning pain in the hands and feet
• blurred vision and other problems with your eyes, such as vision loss that comes and goes
• night sweats
• unusual bleeding, for example, nosebleeds, or you bruise more easily
• itching, especially after a shower or bath, this can be severe - doctors call this pruritus
• pain or discomfort in the tummy (abdomen) from an enlarged spleen
• high blood pressure
• gout - you might have painful, stiff or swollen joints
• bleeding or blood clots, which can sometimes lead to stroke or heart problems
• bone pain
• reddening of the skin
• feeling dizzy
• chest pain
• blood clots - symptoms include pain, redness and swelling around the area where the clot is and it may feel warm to touch, breathlessness, pain in your chest or upper back, or coughing up blood

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.