Polycythemia

Definition:
Polycythemia is defined by a hematocrit and/or a hemoglobin above the normal range. Relative polycythemia must be distinguished from absolute polycythemia. In relative polycythemia, the erythrocyte mass is not increased. The increased hematocrit and/or hemoglobin value occurs because the plasma volume is decreased (e.g. dehydration). In absolute polycythemia, the erythrocyte mass is increased.

Hematology:

The erythrocytes are tightly packed and overlap each other.

Occurrence:
It is important to distinguish the primary form from the secondary form. With the primary form, polycythemia vera is normally present, which is a myeloproliferative disorder. The secondary form develops due to an increased production of erythropoietin caused by chronic hypoxemia (e.g. chronically obstructed pulmonary disease) or (rarely) with an erythropoietin-producing tumor (e.g. kidney tumor, kidney cyst).