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An increase in the number of circulating erythrocytes in the blood above the minimum normal levels.


This condition may be due to the overproduction of red blood cells or due to a chronically low oxygen levels. For instance, individuals living at high altitudes have relatively higher concentration of RBCs in blood than those who are not.

This condition can also be observed in individuals with emphysema, pulmonary insufficiency and heart failure.

Word origin: erythrocyte + Greek -osis (condition).

Synonyms: polycythemia or polycythaemia, erythremia

Compare: erythroblastopenia, leukocytosis, thrombocytosis.