Polycythemia or erythrocytosis is a rare condition that occurs when the body produces too many red blood cells, the components responsible for carrying oxygen from the lungs. When this happens, the blood thickens, which increases the risk of a stroke. Additionally, thicker blood travels more slowly through blood vessels and organs. This issue causes many of the symptoms of secondary polycythemia.
There are two types of polycythemia: primary and secondary. Primary polycythaemia is genetic and most commonly a result of cell mutation in the bone marrow, where red blood cells are created. In secondary polycythemia, a pre-existing condition causes the body to overproduce red blood cells. People with secondary polycythemia typically have excess erythropoietin (EPO), a hormone that drives the formation of red blood cells. Though secondary polycythemia may have a genetic component, it does not cause a mutation in the bone marrow. Alternately, those with primary polycythemia don't have excess EPO.
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