How does polycythemia affect the body?

Over time, polycythemia causes a thickening of the blood. This thickening results in decreased blood flow to body tissues and organs, as well as decreased levels of oxygen being delivered to the body. The symptoms seen in untreated or undiagnosed polycythemia are a result of these low levels of oxygen. In addition, the thickened blood associated with this disorder is likely to clot, leading to complete cut off of blood flow to body organs, including the brain. Without oxygen, tissues and organs are not able to survive. Polycythemia also causes enlargement of the spleen.