Erythrocytosis refers to persistently elevated hemoglobin/hematocrit and/or increased red cell mass—it indicates “more red cells than expected,” but does not identify the cause.

Clinically, erythrocytosis is often framed as: [1][6]

• Relative erythrocytosis: hemoglobin/hematocrit appears high because plasma volume is reduced (e.g., dehydration or diuretic-related hemoconcentration). [1][7]
• Absolute erythrocytosis: true increase in red cell mass, driven by either:
  • Primary (bone-marrow–driven; PV is the key example), or
  • Secondary (a physiologic response to hypoxia or excess erythropoietin signaling, depending on the situation). [1][6]

Erythremia is largely a historical label seen in older reports; many authors used it as a name for PV (Vaquez–Osler disease) or closely related descriptions of that same clinical syndrome. [2][3]

Because the term is not part of modern classification, it can create confusion today—most current sources prefer PV for the diagnosis and erythrocytosis for the lab finding. [4][5]

Polycythemia vera (PV) is a clonal myeloproliferative neoplasm in which bone marrow overproduction leads to primary erythrocytosis, often accompanied by leukocytosis and/or thrombocytosis (“panmyelosis” in marrow). [4][5]

Modern diagnostic frameworks incorporate blood counts, JAK2 mutation status, bone marrow morphology, and serum erythropoietin as part of the overall pattern. [4][5]

• Late 1800s–early 1900s: Early clinical descriptions (linked to Vaquez and Osler) described a syndrome of polycythemia/erythrocytosis with features such as cyanosis and splenomegaly, helping define the clinical picture later recognized as PV. [8][9]
• 1920s–1930s: Publications continued to use “erythræmia/erythremia” in connection with Vaquez-Osler disease / polycythemia rubra vera, reflecting overlapping terminology prior to modern standardization. [10][11]
• Mid-20th century: Diagnostic frameworks increasingly separated erythrocytosis (finding) from PV (disease); PVSG criteria (1967) embedded RCM in diagnostic thinking, and later analyses highlighted that PV diagnosis often does not require RCM when other clinical/lab features are available. [12][13][14]

Using the right term helps match the next step to the situation:

• “Erythrocytosis” signals that a cause still needs to be identified (relative, secondary, or primary). [1]
• PV is a specific diagnosis within modern MPN classification and is managed with an ongoing plan focused largely on reducing thrombotic risk and controlling counts/symptoms. [3][4][15]
• Secondary or relative erythrocytosis may improve when the underlying driver is addressed (depending on the cause). [1]

1. Is erythremia the same as polycythemia vera?

In much of older literature, erythremia was used in a way that overlaps strongly with what we now call PV. Modern practice generally avoids the term to reduce confusion. [2][3]

2. What’s the difference between erythrocytosis and PV?

Erythrocytosis is the finding (elevated hemoglobin/hematocrit and/or red cell mass). PV is a specific clonal marrow disease (MPN) that can cause primary erythrocytosis. [1][4]

3. Why do some old papers say “erythremia (polycythemia vera)”?

Because terminology was not standardized, many authors treated the terms as overlapping or synonymous before modern classification frameworks were widely adopted. [2][3]

PV — Polycythemia vera

MPN — Myeloproliferative neoplasm

JAK2 — Janus kinase 2

PVSG — Polycythemia Vera Study Group

RCM — Red cell mass

FAQs — Frequently asked questions

1. Mithoowani, S., Laureano, M., Crowther, M. A., & Hillis, C. M. (2020). Investigation and management of erythrocytosis. CMAJ, 192(32), E913–E918. https://doi.org/10.1503/cmaj.191587
2. Barker, N. W. (1931). Polycythemia vera and chronic pulmonary disease. Archives of Internal Medicine, 47(1), 94–103. https://doi.org/10.1001/archinte.1931.00140190105010
3. Tefferi, A., Vannucchi, A. M., & Barbui, T. (2021). Polycythemia vera: Historical oversights, diagnostic details, and therapeutic views. Leukemia, 35, 3339–3351. https://doi.org/10.1038/s41375-021-01401-3
4. McMullin, M. F., Harrison, C. N., Ali, S., Cargo, C., Chen, F., Ewing, J., Garg, M., Godfrey, A., Knapper, S., McLornan, D. P., Nangalia, J., Sekhar, M., Wadelin, F., Mead, A. J., & BSH Committee. (2019). A guideline for the diagnosis and management of polycythaemia vera: A British Society for Haematology guideline. British Journal of Haematology, 184(2), 176–191. https://doi.org/10.1111/bjh.15648
5. Barbui, T., Thiele, J., Gisslinger, H., Finazzi, G., Vannucchi, A. M., Tefferi, A., & the authors. (2018). The 2016 WHO classification and diagnostic criteria for myeloproliferative neoplasms: Document summary and in-depth discussion. Blood Cancer Journal, 8(2), 15. https://doi.org/10.1038/s41408-018-0054-y
6. Patnaik, M. M., & Tefferi, A. (2009). The complete evaluation of erythrocytosis: congenital and acquired. Leukemia, 23(5), 834–844. https://doi.org/10.1038/leu.2009.54
7. Lawrence, J. H., & Berlin, N. I. (1952). Relative polycythemia; the polycythemia of stress. The Yale journal of biology and medicine, 24(6), 498–505.
8. Berlin, N. I., & Wasserman, L. R. (1997). Polycythemia vera: a retrospective and reprise. The Journal of laboratory and clinical medicine, 130(4), 365–373. https://doi.org/10.1016/s0022-2143(97)90035-4
9. Osler, W. (2008). Chronic cyanosis, with polycythaemia and enlarged spleen: A new clinical entity. 1903. American Journal of the Medical Sciences, 335(6), 411–417. https://doi.org/10.1097/MAJ.0b013e318175d13d
10. Ryle, J. A. (1922). Case of erythræmia (Vaquez-Osler disease). Proceedings of the Royal Society of Medicine, 15(Clinical Section), 28. https://doi.org/10.1177/003591572201500229
11. Stolkind E. (1933). Erythro-leukæmia (Polycythæmia Rubra Vera-Vaquez's Disease-Associated with Myeloid Leukæmia). Proceedings of the Royal Society of Medicine, 27(1), 19–22. https://doi.org/10.1177/003591573302700104
12. Sirhan, S., Fairbanks, V. F., & Tefferi, A. (2005). Red cell mass and plasma volume measurements in polycythemia: Evaluation of performance and practical utility. Cancer, 104(1), 213–215. https://doi.org/10.1002/cncr.21105
13. Sirhan, S., Fairbanks, V. F., & Tefferi, A. (2005). Red cell mass and plasma volume measurements in polycythemia: Evaluation of performance and practical utility. Cancer, 104(1), 213–215. https://doi.org/10.1002/cncr.21105
14. Pollycove, M. (1998). Haematology. In M. N. Maisey, K. E. Britton, & B. D. Collier (Eds.), Clinical nuclear medicine. Springer. https://doi.org/10.1007/978-1-4899-3356-0_4
15. Tefferi, A., & Barbui, T. (2023). Polycythemia vera: 2024 update on diagnosis, risk-stratification, and management. American Journal of Hematology, 98(9), 1465–1487. https://doi.org/10.1002/ajh.27002