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Polycythemia vera (PV): Overproduction (proliferation) of red blood cells due to bone marrow disease (myeloproferative disorder). PV tends to evolve into acute leukemia or a condition with the marrow replaced by scar tissue (myelofibrosis).
To have PV, there must be polycythemia which formally exists when the hemoglobin, red blood cell (RBC) count, and total RBC volume are all above normal. For example, the hematocrit (the percentage of red blood cells in whole blood), normal range is from about 42 to about 52% in adult males and from about 37 to about 48% in adult females. The hematocrit in polycythemia is significantly above 52% in men and above 48% in females.