Dr Daniel J Bell et al.

Erythrocytosis (or polycythemia) is the presence of an excessive number of red blood cells in the circulation. It can be primary or arise secondarily to another pathology.


Absolute erythrocytosis is defined as a red cell mass which is >125% predicted for sex and age 2.

Although the diagnosis of erythrocytosis is often put forward when the hemoglobin and/or hematocrit are elevated, they can both be raised, especially the former, yet the red cell mass not be abnormal. Nevertheless if the hematocrit is >0.60 in men or 0.56 in women, then an absolute erythrocytosis is certain 3.


Following is a list of primary and secondary causes of erythrocytosis.
Secondary etiologies are much more common 1:

  • erythropoietin receptor (EPOR) mutations
  • high oxygen affinity hemoglobins
    • >100 mutations described
  • abnormal 2,3 bisphosphoglycerate mutase
  • methemoglobinemia
  • dysfunctional oxygen-sensing pathway
    • e.g. VHL mutations


Pathological erythropoietin secretion

Exogenous erythropoietin

  • drug administration (physician-directed or illicit)
    • erythropoietin (EPO)
    • androgens

Article information

rID: 60101
System: Haematology
Synonyms or Alternate Spellings:
  • Polycythemia
  • Secondary polycythaemia
  • Secondary polycythemia
  • Secondary erythrocytosis
  • Compensatory erythrocytosis
  • Compensatory polycythaemia
  • Compensatory polycythemia
  • Polycythaemia

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