Polycythaemia

What is polycythaemia?

Blood is made of different types of cells and a liquid called plasma. In polycythaemia, the concentration of red blood cells in the blood is higher than normal. This may be because there are actually more red blood cells than usual, or because the amount of liquid (plasma) is less than normal.

Causes and risk factors

One form is called primary polycythaemia, also called polycythaemia vera (or PV). This condition occurs if the bone marrow produces too many red blood cells. Over 90 per cent of those affected have a mutation of a gene called the JAK2 gene, which does not seem to cause PV directly but predisposes towards its development. PV is rare, and predominantly affects those aged 60 and older.

The characteristic ruddy-face caused by the high red blood cell concentration is often wrongly assumed by others to be the result of drinking too much alcohol.

Another form is secondary polycythaemia. Once again the bone marrow makes too many red blood cells, but this time it's in response to a lack of oxygen. This may be due to a lung condition such as chronic bronchitis or emphysema (now known as chronic obstructive pulmonary disease, or COPD) or when someone lives at high altitude.

There's a further form, called relative polycythaemia. Although the number of red blood cells is normal, the plasma volume is reduced. Causes can include:

• Stress
• Raised blood pressure
• Being overweight
• Dehydration
• Treatment and recovery

It's important that polycythaemia is investigated and treated, or at least monitored, because the high numbers of red cells in the blood make it thicker and bloods clots are more likely to form. This increases the risk of heart attack, stroke and other problems.

Treatment includes regular removal of some blood to keep the levels of cells down, or medicines which prevent the bone marrow from making too much blood. In secondary polycythaemia, the underlying cause may itself need treatment.

Some people need treatment for symptoms or complications of polycythaemia, too - itching is a common problem, for example. Sufferers of relative polycythemia are usually advised to lose weight, stop smoking and to take medication to bring their blood pressure down to normal levels.