Mayo Clinic (Definition)
Polycythemia vera is a blood disorder in which your bone marrow makes too many red blood cells. Polycythemia vera also may result in production of too many of the other types of blood cells â€” white blood cells and platelets. But it's the excess red blood cells that thicken your blood and cause most of the concerns associated with polycythemia vera.
Polycythemia vera â€” also called primary polycythemia â€” is rare and usually develops slowly. You may have it for years without noticing signs or symptoms. Often, polycythemia vera is found during a blood test done for some other reason.
Without treatment, polycythemia vera can be life-threatening. However, with proper medical care, many people experience few problems related to this disease.