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.
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.
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.
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 fluid loss.
As the condition cannot be cured, treatment focuses on treating symptoms and reducing thrombotic complications reducing the erythrocyte levels.
Blood letting or phlebotomy is one form of treatment, which often may be combined with other therapies. The removal of blood from the body reduces the blood volume and brings down the hematocrit levels.
Low dose aspirin is often prescribed. Research has shown that aspirin reduces the risk for various thrombotic complications.
Chemotherapy for polycythemia may be used sparingly, when the rate of bloodlettings required to maintain normal hematocrit is not acceptable. This is usually with a "cytoreductive agent" (hydroxyurea, also known as hydroxycarbamide).
The tendency to avoid chemotherapy if possible, especially in young patients, is due to research indicating increased risk of transformation to AML, and while hydroxyurea is considered safer in this aspect, there is still some debate about its long-term safety.
In the past, injection of radioactive isotopes was used as another means to suppress the bone marrow. Such treatment is now avoided due to a high rate of AML transformation.
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