INDEPENDENCE DAY. On July 4, 1776, the thirteen colonies claimed their independence from England, an event which eventually led to the formation of the United States.
Polycythemia vera is a rare, chronic disorder involving the overproduction of blood cells in the bone marrow (myeloproliferation). The overproduction of red blood cells is most dramatic, but the production of white blood cells and platelets are also elevated in most cases.
Video: Polycythemia: Definition & Causes. Polycythemia is a blood disorder in which the body produces too many blood cells as a result of a problem with the bone marrow or an increased production of the hormone erythropoietin. Learn about the causes of polycythemia.