Types of polycythaemia

Increased red cell concentration can be:

• absolute
  • primary - polycythaemia rubra vera - primary defect in the marrow stem cell population causing erythrocytosis irrespective of physiological needs
  • secondary - normal marrow stem cells respond to elevated erythropoietin or erythropoietin-like substances in the blood, however appropriate
    • congenital e.g. - Chuvash erythrocytosis (VHL gene mutation), high oxygen-affinity haemoglobin
    • acquired e.g. - hypoxia driven, pathologic erythropoietin production or exogenous erythropoietin
  • idiopathic - no cause for erythrocytosis can be identified, in this group around one third will have lower erythropoietin levels than normal and the rest have inappropriately normal levels for elevated haemoglobin or raised erythropoietin (2)
• apparent - normal or minimally raised red cell volume with a reduced plasma volume

Note - the WHO classification and the ICC now categorise polycythaemia vera as a subtype of myeloproliferative neoplasms (MPNs). (2,3)

Reference

1. Tefferi A, Barbui T. Polycythemia vera: 2024 update on diagnosis, risk-stratification, and management. Am J Hematol. 2023 Sep;98(9):1465-87.
2. Khoury JD, Solary E, Abla O, et al. The 5th edition of the World Health Organization classification of haematolymphoid tumours: myeloid and histiocytic/dendritic neoplasms. Leukemia. 2022 Jul;36(7):1703-19.
3. Arber DA, Orazi A, Hasserjian RP, et al. International consensus classification of myeloid neoplasms and acute leukemias: integrating morphologic, clinical, and genomic data. Blood. 2022 Sep 15;140(11):1200-28.