Polycythemia is a condition in which there is a net increase in the total circulating erythrocyte (red blood cell) mass of the body. There are several types of polycythemia. more...
Primary polycythemia (also known as polycythemia vera)
Primary polycythemia, often called polycythemia vera (PCV), polycythemia rubra vera (PRV), erythremia, or just PV, occurs when excess erythrocytes are produced as a result of a proliferative abnormality of the bone marrow. This can also be brought on by abnormalities (tumors) in the kidneys or other growths since the kidney helps to regulate erythrocytes production. Often, excess white blood cells (leukocytosis) and platelets (thrombocytosis) are also produced. It is, therefore, classified as a myeloproliferative disease.
In primary polycythemia there may be 8 to 9 million and occasionally 11 million erythrocytes per cubic millimeter of blood, and the hematocrit may be as high as 70 to 80%. In addition, the total blood volume sometimes increases to as much as twice normal. The entire vascular system can become markedly engorged with blood, and circulation times for blood throughout the body can increase up to twice the normal value. The increased numbers of erythrocytes can increase the viscosity of the blood to as much as five times normal. Capillaries can become plugged by the very viscous blood, and the flow of blood through the vessels tends to be extremely sluggish.
Recently, in 2005, a mutation in the JAK2 kinase (V617F) was found by multiple research groups (Baxter et al., 2005; Levine et al., 2005) to be strongly associated with polycythemia vera. JAK2 is a member of the Janus kinase family. This mutation be helpful in making a diagnosis or as a target for future therapy.
As a consequence of the above, people with untreated PV are at a risk of various thrombotic events (deep venous thrombosis, pulmonary embolism), heart attack and stroke, and have a substantial risk of Budd-Chiari syndrome (hepatic vein thrombosis). The condition is considered chronic; no cure exists. Symptomatic treatment (see below) can normalize the blood count and most patients can live a normal life for years.
Secondary polycythemia is caused by either appropriate or inappropriate increases in the production of erythropoietin that result in an increased production of erythrocytes. In secondary polycythemia their may be 6 to 8 million and occasionally 9 million erythrocytes per cubic millimeter of blood. A type of secondary polycythemia in which the production of erythropoietin increases appropriately is called physiologic polycythemia. Physiologic polycythemia occurs in individuals living at high altitudes (4275 to 5200 meters), where oxygen availability is less than at sea level. Such people may have 6 to 8 million erythrocytes per cubic millimeter of blood. It is because of this that Lance Armstrong trains in the mountains to prepare for bicycle races.
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