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Polycythemia Vera Lab Values: What Is and Isn’t PV

Feb 9, 2026

Key takeaways

  • High red blood cell (RBC) counts, hemoglobin (Hgb), or hematocrit (Hct) can occur for many reasons, and an abnormal value alone doesn’t diagnose polycythemia vera (PV). [1]
  • PV is suggested by a persistent erythrocytosis pattern (elevated Hgb/Hct or increased red cell mass) plus a JAK2 mutation, with bone marrow findings and often low serum erythropoietin (EPO) supporting the diagnosis. [2]
  • Dehydration/hemoconcentration, smoking-related hypoxia, chronic lung disease or sleep apnea, and high-altitude exposure are common alternatives; the overall lab pattern helps clinicians separate PV from secondary or relative causes. [3]

Overview

Routine bloodwork is often the first clue that red cell measures are higher than expected. Elevated RBC count, Hgb, or Hct can be transient (for example, from dehydration) or reflect a sustained medical condition. Polycythemia vera (PV) is a myeloproliferative neoplasm in which the bone marrow produces too many blood cells—most prominently red blood cells—and this process is typically associated with an acquired JAK2 mutation. [4][5]

The core polycythemia vera lab values

When PV is present, clinicians usually see a consistent pattern over time, not a one-off abnormal result. WHO diagnostic frameworks emphasize elevated Hgb/Hct, JAK2 mutation, and characteristic bone marrow morphology, with subnormal EPO as a supportive (minor) criterion. [2]

Test

Typical finding in PV [2]

Why it happens

Hemoglobin / Hematocrit

Often above diagnostic thresholds (e.g., Hgb >16.5 g/dL men, >16.0 g/dL women; or Hct >49% men, >48% women, depending on criteria used)

Reflects increased red cell mass [6]

Erythropoietin (EPO)

Often low/subnormal

Physiologic suppression of EPO in the setting of increased red cells [7]

JAK2 (V617F or exon 12)

Positive in the great majority (> 95%) of PV [4]

A driver mutation that supports the diagnosis of PV [2]

Bone marrow biopsy

Hypercellular marrow with trilineage growth (panmyelosis)

unregulated neoplastic proliferation produces panmyelosis [8]


When high RBC, hemoglobin, or hematocrit doesn’t mean PV

Many conditions can raise red cell measures, but the mechanism is different.


1. High RBC/Hgb/Hct with normal or high EPO

This pattern more often suggests secondary erythrocytosis (the body is responding to a stimulus, commonly low oxygen).

  • Patients with smoking, hypoxemia (chronic lung disease, sleep apnea, high-altitude exposure, and certain cardiac shunts), or tumors (EPO-producing kidney or other tumors) have elevated or abnormal EPO levels. [3]
  • Key lab clue: EPO is not low, unlike the supportive pattern often seen in PV. [3]


2. High hemoglobin or hematocrit with no true increase in red cell mass

Sometimes the red cells aren’t truly elevated; instead, plasma (the liquid part of blood) volume is reduced, concentrating the blood (relative polycythemia/hemoconcentration).

  • Common triggers include dehydration, diuretics, and stress-related hemoconcentration (often described as Gaisböck syndrome). [9][10]
  • Key lab clue: values may normalize with rehydration and correction of contributing factors. [10]


Lab patterns and the clinical clues

Lab Pattern

Clinical clues

Follow-up review

High Hgb/Hct + low EPO (± panmyelosis)

Primary marrow process

Targeted confirmatory testing might be needed (e.g., JAK2 review ± marrow if indicated)[4][11]

High Hgb/Hct + normal/high EPO + hypoxia risk factors

Oxygen-driven physiology (secondary erythrocytosis)

Oxygenation (pulse oximetry), sleep or lung risk factors, altitude exposure, and medications.[9][12]

High Hct + normal EPO + reversible plasma-volume loss

Hemoconcentration

(relative polycythemia);

Hydration status, diuretic use, and repeat testing. [1][9]


Managing high RBC and PV lab results

If polycythemia vera is confirmed, a common foundational strategy is phlebotomy and low-dose aspirin (if no contraindications) with tight Hct control, because maintaining Hct <45% has been associated with lower rates of cardiovascular death and major thrombosis in randomized evidence. [13][14] Cytoreductive therapy (e.g., hydroxyurea or interferon-based approaches) may be used based on risk profile, symptoms, and clinician judgment. [5][15]


For non-PV causes, treatment focuses on the driver (e.g., correcting dehydration, addressing sleep apnea, adjusting contributing medications) and monitoring the response. [3][9]

Final thoughts

A high RBC, hemoglobin, or hematocrit result should be interpreted in context. PV is one important cause of persistent elevation, but clinicians typically rely on a pattern that includes JAK2 mutation testing, bone marrow findings, and EPO/oxygenation assessment to distinguish PV from secondary or relative causes. [3][4]


If your results are repeatedly high, follow up with a hematology team to ensure appropriate testing and a clear diagnosis.

References

  1. Pillai, A. A., Fazal, S., Mukkamalla, S. K. R., & Babiker, H. M. (2023). Polycythemia. In StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK526081/
  2. Thiele, J., Kvasnicka, H. M., Gianelli, U., Arber, D. A., Tefferi, A., Vannucchi, A. M., Barbui, T., & Orazi, A. (2025). Evolution of WHO diagnostic criteria in “Classical Myeloproliferative Neoplasms” compared with the International Consensus Classification. Blood Cancer Journal, 15(1), 31. https://doi.org/10.1038/s41408-025-01235-7
  3. Lekovic, D., Sobas, M., & Lucijanic, M. (2025). Editorial: Differential diagnosis of erythrocytosis and analysis of their clinical utility. Frontiers in Medicine, 12, 1742762. https://doi.org/10.3389/fmed.2025.1742762
  4. Nathany, S., Koulmane Laxminarayana, S. L., Tewari, S., Belurkar, S., Khanna, R., & Manohar, C. (2020). Impact of World Health Organization (WHO) Revised Criteria-2016 on the Diagnosis of Polycythemia Vera. Indian journal of hematology & blood transfusion : an official journal of Indian Society of Hematology and Blood Transfusion, 36(3), 477–483. https://doi.org/10.1007/s12288-019-01202-w
  5. Tefferi, A., & Barbui, T. (2023). Polycythemia vera: 2023 update on diagnosis, risk-stratification, and management. American Journal of Hematology, 98(7), 1465–1487. https://doi.org/10.1002/ajh.27002
  6. 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
  7. Tefferi, A. (1999). Diagnosing polycythemia vera: A paradigm shift. Mayo Clinic Proceedings, 74(2), 159–162. https://doi.org/10.4065/74.2.159
  8. Barbui, T., Thiele, J., Gisslinger, H., Kvasnicka, H. M., Vannucchi, A. M., Guglielmelli, P., Orazi, A., & Tefferi, A. (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 IF: 11.6 Q1 B1
  9. Lu, X., & Chang, R. (2023). Polycythemia vera. In StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK557660/
  10. Haider, M. Z., & Anwer, F. (2023). Secondary polycythemia. In StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK562233/
  11. da Silva, A. M. (2013). Dealing with polycythemia in primary care. Korean Journal of Family Medicine, 34(1), 66–73. https://doi.org/10.4082/kjfm.2013.34.1.66
  12. Marchioli, R., Finazzi, G., Specchia, G., Cacciola, R., Cavazzina, R., Cilloni, D., De Stefano, V., Elli, E., Iurlo, A., Latagliata, R., Lunghi, F., Lunghi, M., Marfisi, R. M., Musto, P., Masciulli, A., Musolino, C., Cascavilla, N., Quarta, G., Randi, M. L., Rapezzi, D., … CYTO-PV Collaborative Group (2013). Cardiovascular events and intensity of treatment in polycythemia vera. The New England journal of medicine, 368(1), 22–33. https://doi.org/10.1056/NEJMoa1208500
  13. Landolfi, R., Marchioli, R., Kutti, J., Gisslinger, H., Tognoni, G., Patrono, C., Barbui, T., & European Collaboration on Low-Dose Aspirin in Polycythemia Vera Investigators (2004). Efficacy and safety of low-dose aspirin in polycythemia vera. The New England journal of medicine, 350(2), 114–124. https://doi.org/10.1056/NEJMoa035572
  14. Marchetti, M., et al. (2022). Appropriate management of polycythaemia vera with cytoreductive drug therapy: European LeukemiaNet 2021 recommendations. The Lancet Haematology, 9(4), e301–e311. https://doi.org/10.1016/S2352-3026(22)00046-1
  15. Barosi, G., Mesa, R., Finazzi, G., Harrison, C., Kiladjian, J.-J., Lengfelder, E., McMullin, M. F., Passamonti, F., Vannucchi, A. M., Besses, C., Gisslinger, H., Samuelsson, J., Verstovsek, S., Hoffman, R., Pardanani, A., Cervantes, F., Tefferi, A., & Barbui, T. (2013). Revised response criteria for polycythemia vera and essential thrombocythemia: An ELN and IWG-MRT consensus project. Blood, 121(23), 4778–4781. https://doi.org/10.1182/blood-2013-01-478891