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Erythrocytosis is a condition in which there is an abnormally high number of red blood cells, or erythrocytes, in the circulation. What is called primary erythrocytosis may be caused by a rare bone marrow disorder, known as polycythemia vera, where the bone marrow produces too many red cells. More commonly, what is known as secondary erythrocytosis occurs. This is usually the result of an existing medical disorder, such as a long-term lung disease, where tissues have become starved of oxygen and high levels of a protein known as erythropoietin have been released, stimulating red blood cell production. What is called apparent erythrocytosis may also occur, where the overall volume of blood plasma is decreased, making the red blood cells appear more concentrated.
Whatever the cause of the condition, symptoms may not be apparent in the early stages and the condition may be discovered from routine blood tests. Vague symptoms such as tiredness may be present and sometimes sweating, itching, dizziness and headaches may be experienced. For people who have polycythemia vera, there is an increased risk of blood clots occurring and in some cases the first sign of the condition may be a thrombosis, or clot, inside a blood vessel, causing a problem such as a stroke or heart attack. The UK spelling of polycythemia vera is polycythaemia vera, and it may also be known as polycythaemia rubra vera.
People who have secondary erythrocytosis may also have a greater risk of thrombosis but it is thought to be less than for those who have polycythemia vera. It is not known whether having apparent erythrocytosis increases a person's thrombosis risk. Reductions in blood plasma volume, which lead to an apparent increase in red blood cells, may be caused by alcoholism, heavy smoking or the use of diuretic drugs which remove fluid from the body.
The treatment depends on the cause. Secondary forms of the condition require treatment of the underlying disorder, and the outlook will depend on how successful this is. In the case of a long-term lung disease, giving oxygen may help reduce the levels of erythropoietin and decrease red blood cell numbers.
For the primary condition, if the rare blood disease polycythemia vera is the cause, the outlook is poor without treatment. There is a high risk of a fatal stroke or heart attack occurring within 18 months. With treatment, the outlook improves to give an estimated life expectancy of about 20 years. Treatment methods include removing blood from the circulation, taking aspirin to lower the risk of clotting and taking medication to lower the number of blood cells.