Polycythemia

Polycythemia
Classification and external resources
Packed cell volume diagram.
ICD-10	D75.1, P61.1
ICD-9	289.0, 776.4
DiseasesDB	10295
eMedicine	Ped/1848
MeSH	D011086

Polycythemia (or polycythaemia) is a condition in which there is an increase in the proportion of blood volume that is occupied by red blood cells, which is measured as hematocrit level.

It can be due to an increase in the mass of red blood cells^[1] ("absolute polycythemia") or to a decrease in the volume of plasma ("relative polycythemia").^[2]

Absolute polycythemia

The overproduction of red blood cells may be due to a primary process in the bone marrow (a so-called myeloproliferative syndrome), or it may be a reaction to chronically low oxygen levels or, rarely, a malignancy.

Primary polycythemia (Polycythemia vera)

Primary polycythemia, often called polycythemia vera (PCV), polycythemia rubra vera (PRV), or erythremia, occurs when excess red blood cells are produced as a result of an abnormality of the bone marrow.^[3] Often, excess white blood cells and platelets are also produced. Polycythemia vera is classified as a myeloproliferative disease. Symptoms include headaches and vertigo. Signs on physical examination include an abnormally enlarged spleen and/or liver. In some cases, affected individuals may have associated conditions including high blood pressure or the formation of blood clots. Transformation to acute leukemia is rare. Phlebotomy is the mainstay of treatment. A hallmark of polycythemia is an elevated hematocrit, with Hct > 55% seen in 83% of cases.^[4] Mutations in JAK2 are found in 95% of cases, though also present in other myeloproliferative disorders.^[5]

Secondary polycythemia

Secondary polycythemia is caused by either natural or artificial increases in the production of erythropoietin, hence an increased production of erythrocytes. In secondary polycythemia, there may be 6 to 8 million and occasionally 9 million erythrocytes per cubic millimeter (microliter) of blood. Secondary polycythemia resolves when the underlying cause is treated.

Secondary polycythemia in which the production of erythropoietin increases appropriately is called physiologic polycythemia. This physiologic (meaning normal) polycythemia is a normal adaptation to living at high altitudes (see altitude sickness). Many athletes train at high altitude to take advantage of this effect — a legal form of blood doping. Similarly, athletes with primary polycythemia may have a competitive advantage due to greater stamina.^{[citation needed]}

Other causes of secondary polycythemia include smoking, renal or liver tumors, hemangioblastomas in the central nervous system, heart or lung diseases that result in hypoxia, and endocrine abnormalities including pheochromocytoma and adrenal adenoma with Cushing's syndrome. People whose testosterone levels are high because of the use anabolic steroids, including athletes who abuse steroids and people whose doctors put them on doses that are too high, as well as people who take erythropoietin may develop secondary polycythemia.

Secondary polycythemia can be induced directly by phlebotomy to withdraw some blood, concentrate the erythrocytes, and return them to the body.

Chuvash polycythemia

Chuvash polycythemia refers to a familial form of erythrocytosis different from classical polycythemia vera. This involved patients from Chuvashia and is associated with a C598T mutation in the von Hippel-Lindau gene (VHL).^[6] A cluster of patients with Chuvash polycythemia have been found in other populations, such as on the Italian island of Ischia, located in the Bay of Naples.

Relative polycythemia

Relative polycythemia is an apparent rise of the erythrocyte level in the blood; however, the underlying cause is reduced blood plasma. Relative polycythemia is often caused by loss of body fluids, such as through burns, dehydration and stress.

See also

• Cytopenia, a decrease in blood cell count

References