condition in which there is a net increase in the number of red blood cells. Overproduction of red blood cells may be due to a primary process in the bone marrow (a so-called myeloproliferative syndrome), or it may be a reaction to chronically low oxygen levels or, rarely, a malignancy. Often asymptomatic. Classic symptom of polycythemia vera (in 40%) is generalized itching, particularly after exposure to warm water, which may be due to abnormal histamine release or prostaglandin production. [ Wikipedia ]
