A blood disorder in which there is an increased concentration of red blood cells
In polycythaemia, the concentration of red blood cells is increased. The condition may be due to increased red blood cell production or decreased volume of the fluid part of blood (plasma), leading to a high concentration of red cells.
There are three types of polycythaemia: primary, secondary, and stress.
In primary polycythaemia, which is also known as true polycythaemia or polycythaemia vera, the production of red blood cells in the bone marrow is increased as a result of a mutation (change) in a gene called the JAK2 gene, which is involved in the regulation of red blood cell production. This type of polycythaemia is rare and usually only affects people over the age of 60.
In secondary polycythaemia, there is also increased production of red cells by the bone marrow. In this case, the cause is a low oxygen level in the blood, which can occur for several reasons. For example, it can develop in people living at high altitudes, where oxygen levels are naturally low. It may also occur if the uptake of oxygen by the blood is impaired due to heavy smoking or lung disorders such as chronic obstructive pulmonary disease.
In stress polycythaemia, production of red cells is normal but the volume of blood plasma is decreased. This change in the composition of blood may result from dehydration. It may also occur in people who are obese or abuse alcohol.
All types of polycythaemia cause similar symptoms. They may include:
A ruddy complexion, together with bloodshot eyes.
Headache and ringing in the ears (see Tinnitus).
Blurred vision and dizziness.
Primary polycythaemia may also produce itching, especially after a hot bath. The spleen may enlarge, causing abdominal discomfort and there may also be prolonged bleeding or increased blood clotting.
Your doctor may arrange for a blood test to measure the concentrations of red cells in the blood and a bone marrow aspiration and biopsy to look for increased red cell production. You may also have a lung function test to look for an underlying cause, and possibly a blood test to check for the presence of a mutated JAK2 gene.
If you have secondary or stress polycythaemia, the treatment is directed at the underlying cause.
Venesection (needle puncture of a vein) may be used to treat primary polycythaemia. At least 300 ml (10 fl oz) of blood are removed from the circulation each week until the levels of red cells are normal. Oral chemotherapy may also be used to reduce the production of red blood cells. With treatment, most people live for 10–15 years after diagnosis. Rarely, primary polycythaemia may develop into another bone marrow disorder, such as acute leukaemia.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.