Polycythaemia (see also ERYTHROCYTOSIS). A rise in the amount of HAEMOGLOBIN in the blood. This may be caused by an excessive number of ERYTHROCYTES being produced in the BONE MARROW, or result from a fall in the total volume of PLASMA in the circulatory system. It may also be a response to reduced oxygen levels – for example, among people living at high altitudes – or to liver or kidney disease: this type is called secondary polycythaemia.

The disorder may, however, occur for no obvious reason and is then called polycythaemia vera. The blood thickens, the sufferer may develop high blood pressure, flushing, headaches, itching and an enlarged spleen. A stroke may occur later in the disease process. Treatment of polycythaemia vera is by regular removal of blood by VENESECTION, sometimes in combination with an anticancer drug. Secondary polycythaemia is treated by remedying the underlying cause.