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Polycythaemia, or erythrocytosis, means having a high concentration of red blood cells in your blood.
This makes the blood thicker and less able to travel through blood vessels and organs. Many of the symptoms of polycythaemia are caused by this sluggish flow of blood.
Mild cases of polycythaemia may not cause any problems, but some people with polycythaemia can experience:
You should make an appointment to see your GP if you have persistent symptoms of polycythaemia.
The slow blood flow associated with polycythaemia can also cause blood clots. These can be serious because they may put you at risk of life-threatening problems such as:
In some cases, a blood clot – known as deep vein thrombosis (DVT) – may form in your leg, before moving elsewhere in your body. Signs of DVT or a pulmonary embolism can include:
If you experience any of the above symptoms, seek medical help immediately. You should also seek emergency medical help if you think that you or someone you're with is having a heart attack or stroke.
Polycythaemia can be divided into several different types, depending on the underlying cause of the condition. In some cases, an underlying cause can't be identified.
"Apparent polycythaemia" is where your red cell count is normal, but you have a reduced amount of a fluid called plasma in your blood, making it thicker.
The condition is often caused by being overweight, smoking, drinking excessive amounts of alcohol or taking certain medications – such as diuretics. A similar condition that's sometimes called "relative polycythaemia" can also occur as a result of dehydration.
Apparent polycythaemia may improve if the underlying cause is identified and managed. Stopping smoking or reducing your alcohol intake, for example, may help.
"Absolute polycythaemia" is where your body produces too many red blood cells. There are two main types:
Both PV and secondary polycythaemia are described in more detail below.
PV is a rare condition usually caused by a fault in the JAK2 gene, which causes the bone marrow cells to produce too many red blood cells.
The affected bone marrow cells can also develop into other cells found in the blood, which means that people with PV may also have abnormally high numbers of both platelets (thrombocytosis) and white bloods cells (leukocytosis).
Although caused by a genetic fault, PV isn't usually inherited. Most cases develop later in life, with 60 the average age of diagnosis.
Secondary polycythaemia is where an underlying condition causes more erythropoietin to be produced. This is a hormone produced by the kidneys that stimulates the bone marrow cells to produce red blood cells.
Conditions that can cause secondary polycythaemia include:
Polycythaemia can be diagnosed by carrying out a blood test to check:
A high concentration of red blood cells suggests you have polycythaemia.
Your GP may have ordered a blood test because you reported some of the above symptoms or complications, but polycythaemia is sometimes only discovered during a routine blood test for another reason.
Your GP may refer you to a haematologist (a specialist in conditions affecting the blood) for more tests, to confirm the diagnosis and to determine the underlying cause.
These may include a blood test to look for the faulty JAK2 gene and an ultrasound scan of your abdomen to look for problems in your kidneys.
Treatment for polycythaemia aims to prevent symptoms and complications (such as blood clots), and treat any underlying causes.
Some of the main treatments used are described below.
Venesection is the simplest and quickest way of reducing the number of red cells in your blood. It may be recommended if you have PV, a history of blood clots, or symptoms suggesting your blood is too thick (see above).
Venesection involves removing about one pint (half a litre) of blood at a time, in a similar way to the procedure used for blood donation.
How often this is needed will be different for each person. At first, you may need the treatment every week, but once your condition is under control you may only need it every 6-12 weeks or less.
For more information, read an NHS leaflet on having a venesection (PDF, 335kb).
In cases of PV, medication may be prescribed to slow down the production of red blood cells.
Many different medications are available and your specialist will take into account your age and health, response to venesection and red blood cell count when choosing the most appropriate one for you. Examples include:
If you have PV, daily low-dose aspirin tablets may be prescribed to help prevent blood clots and reduce the risk of serious complications.
You may also be offered treatment with low-dose aspirin if you have apparent or secondary polycythaemia and another condition affecting your blood vessels, such as coronary heart disease or cerebrovascular disease.
Some people may also need treatment for any other symptoms or complications of polycythaemia they have, or for any underlying cause of the condition.
For example, you may be given medication to help relieve itching, manage COPD or treat gout. Read more about:
As well as improving some cases of apparent polycythaemia, making healthy lifestyle changes can also reduce your risk of potentially serious blood clots for people with all types of polycythaemia.
Having polycythaemia means you're already at high risk of a blood clot, and being overweight or smoking only increases this risk.
You may find the following advice and information helpful:
The outlook for polycythaemia largely depends on the underlying cause.
Many cases are mild and may not lead to any further complications. However, some cases – particularly cases of PV – can be more serious and require long-term treatment.
If well controlled, polycythaemia shouldn't affect your life expectancy, and you should be able to live a normal life. However, people with PV can have a slightly lower life expectancy than normal due to the increased risk of problems, such as heart attacks and strokes.
PV can also sometimes cause scarring of the bone marrow (myelofibrosis), which can eventually lead to you having too few blood cells. In some rare cases, the condition can develop into a type of cancer called acute myeloid leukaemia (AML).
If you have polycythaemia, it's important to take any medication you're prescribed and keep an eye out for signs of possible blood clots to help reduce your risk of serious complications.
If you have polycythaemia, your clinical team will pass information about you on to the National Congenital Anomaly and Rare Diseases Registration Service (NCARDRS).
This helps scientists look for better ways to prevent and treat this condition. You can opt out of the register at any time.