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What is Polycythaemia Vera?

Polycythaemia vera (PV) occurs when too many red blood cells are made.

Polycythaemia vera (PV) is a disorder of the bone marrow that causes an overproduction of red blood cells as well as increased amounts of white blood cells and platelets. 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 may lead to complications such as heart attacks or strokes.


Thicker blood doesn't flow as quickly to your body as normal blood, and the slower blood flow prevents your organs from getting enough oxygen, which can cause other serious problems such as angina and heart failure.


An enlarged spleen (splenomegaly) is a problem affecting up to 36% of patients. When the bone marrow does not function correctly, the spleen compensates by producing red blood cells (known as extra medullary erythropoiesis), causing it to enlarge. The liver may also be affected and become enlarged (this is called hepatomegaly).


Click here to find out more about the symptoms of PV.


Blood clots are also a common complication with PV, affecting around 30% of patients. They are also the most serious complication because they may cause heart attacks and strokes.




A cross section of bone (marrow)

Bone marrow is the soft, spongy tissue that fills the inner cavities of the bone. It’s where red blood cells, white blood cells and platelets are formed. It also contains fluid, blood vessels and fat.


The bone marrow is either red or yellow. When we are born, we only have red marrow, which is responsible for creating new blood cells. As we get older, some of the red marrow is replaced by yellow marrow, which is largely fat. A healthy adult has both red and yellow marrow.

How rare is polycythaemia vera?

PV is a chronic, rare condition that usually affects patients over 55 years, and is very rare in children and patients under the age of 40.


The annual incidence of PV is 2 cases per 100,000 people. PV affects more men than women.