polycythemia

[POLY- + CYT(O)- + -HEMIA.]

An increase in blood volume as a result of an increase in the number of red blood cells, the erythrocytes. It may result from a blood-forming disease that increases cell production, or it may be a physiologic response to an increased need for oxygenation in high altitudes, cardiac disease, or respiratory disorders.

An increase in the circulating red blood cell mass.
There are two distinct forms:
Primary polycythemia is a myeloproliferative disorder of unknown etiology. It occurs as an inherited defect in cattle and is a rare disease in dogs and cats. There is hyperplasia of the cell-forming tissues of the bone marrow, with resultant elevation of the erythrocyte count and hemoglobin level, and an increase in the number of leukocytes and platelets. Called also polycythemia vera.
Secondary polycythemia is a physiological condition resulting from a decreased oxygen supply to the tissues, caused by living at high altitudes, heart disease, circulatory insufficiency or severe pulmonary disease, or the production of erythropoietin or erythropoietin-like compounds, as in polycystic kidney disease, hydronephrosis or renal neoplasms.

• absolute p. — an increase in total hemoglobin and red cell mass with a normal plasma volume. May be a primary or secondary polycythemia.
• compensatory p. — a secondary polycythemia, occurring in response to impairment of oxygenation.
• familial p. — occurs as an autosomal recessive trait in Jersey cattle. See primary polycythemia (above).
• inherited p. — an inherited defect of cattle. Clinically there is dyspnea.
• relative p. — apparent polycythemia resulting from loss of plasma and the hemoconcentration that follows. Called also spurious polycythemia.
• p. vera — see primary polycythemia (above).