DefinitionPolycythemia vera is an abnormal increase in the number of blood cells (primarily red blood cells) produced by the bone marrow.Alternative NamesPrimary polycythemia; Polycythemia rubra vera; Myeloproliferative disorder; Erythremia; Splenomegalic polycythemia; Vaquez's disease; Osler's disease; Polycythemia with chronic cyanosis - Myelopathic polycythemia; Erythrocytosis megalosplenica; Cryptogenic polycythemiaCauses, incidence, and risk factorsPolycythemia vera is a disorder of the bone marrow. It causes too much production of white blood cells, red blood cells, and platelets.It is a rare disease that occurs more often in men than women, and is rare in patients under age 40. The exact cause is unknown.SymptomsBreathing difficulty when lying downDizzinessFullness in the left upper