Polycythaemia
Polycythaemia is a condition in which the body produces too many red blood cells, making the blood thicker than normal. This can slow blood flow and increase the risk of blood clots.
Polycythaemia vera is a rare type caused by a gene mutation in the bone marrow. Secondary polycythaemia can result from chronic low oxygen levels, such as in people with long-standing lung disease, or from living at high altitude.
Symptoms may include headaches, blurred vision, red skin (particularly on the face), itching after a bath, tiredness and dizziness.
A full blood count showing a raised haematocrit (the proportion of blood made up of red cells) and elevated red cell count can indicate polycythaemia. Further tests are needed to distinguish between the different types and guide treatment.
Causes of Polycythaemia
Polycythaemia has two main categories:
- Polycythaemia vera (PV) is caused by a mutation in the JAK2 gene in bone marrow stem cells. This mutation, found in around 95% of PV cases, causes uncontrolled production of red blood cells. PV is a type of myeloproliferative neoplasm
- Secondary polycythaemia is caused by an underlying condition that stimulates increased red blood cell production, usually through elevated erythropoietin (EPO). Causes include chronic obstructive pulmonary disease (COPD), sleep apnoea, living at high altitude, congenital heart disease, kidney disease and, rarely, EPO-producing tumours
Apparent or relative polycythaemia can also occur due to dehydration, which reduces plasma volume and makes the red cell count appear high relative to the total blood volume. This is sometimes seen in heavy smokers and is known as Gaisböck syndrome.
Tests that can help check this condition
Learn more on the official NHS page .
