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High Hemoglobin Causes: Why It Happens and How Polycythemia Vera Plays a Role

Feb 14, 2026

Key takeaways

  • High hemoglobin means your blood test shows a higher-than-expected amount of the oxygen-carrying protein in red blood cells.
  • Causes include temporary concentration changes (like dehydration) and true erythrocytosis from lower oxygen exposure (e.g., high altitude, chronic lung disease, sleep apnea, smoking) or a bone-marrow condition such as polycythemia vera (PV). [1,2,3]
  • The right next step is finding the cause, because the approach differs for relative (concentration) vs absolute (increased red-cell production) causes. [1,3]

Overview

Hemoglobin (Hb) is the protein inside red blood cells that carries oxygen. A “high hemoglobin” result can occur when plasma volume is reduced (so blood is more concentrated) or when the body produces more red blood cells in response to low oxygen or (less commonly) because of a primary bone-marrow disorder such as PV. [1,2,3]


Clinicians typically interpret Hb alongside hematocrit, repeat CBCs, medical history (altitude, smoking, lung/sleep symptoms, medications), and targeted testing when appropriate. [1,3]

Common causes of high hemoglobin

1. Dehydration (relative erythrocytosis)

Fluid loss (e.g., vomiting/diarrhea, heavy sweating, diuretics) can reduce plasma volume and raise Hb/Hct temporarily without increasing total red-cell mass. [1]


2. High altitude

Lower ambient oxygen at altitude can drive a physiologic increase in red blood cell production, which may raise Hb over time. [1,4]


3. Chronic lung disease and sleep-disordered breathing

Conditions that lower oxygen levels (e.g., COPD) and obstructive sleep apnea can be associated with erythrocytosis in some people. [5,6]


4. Smoking

Carbon monoxide from smoking increases carboxyhemoglobin and can contribute to tissue hypoxia, which may stimulate higher red-cell production in long-term exposure. [7]


5. Medications or hormones

Some therapies (notably testosterone) can increase hemoglobin/hematocrit and require periodic monitoring. [8]

Erythropoiesis-stimulating agents (ESAs) can raise hemoglobin and are dosed and monitored carefully in clinical practice due to safety concerns at higher Hb targets. [9,10].


6. Inherited causes

Rare hemoglobin variants with increased oxygen affinity can reduce oxygen delivery to tissues and lead to erythrocytosis; specialized testing (e.g., P50/oxygen dissociation) may be used in selected cases. [11]


7. Polycythemia vera (PV) — A primary bone marrow cause

PV is a myeloproliferative neoplasm characterized by increased red-cell production and often involves a JAK2 variant. [2,12] Symptoms can be absent or nonspecific; reported features can include headache, dizziness, and itching after bathing, among others. [13]


Because PV carries an increased risk of thrombosis, management typically focuses on reducing thrombotic risk (e.g., maintaining hematocrit control, antiplatelet therapy when appropriate, and cytoreduction in selected patients) under clinician supervision. [12,14]

When to see a doctor

Seek medical evaluation if your hemoglobin is persistently above your lab’s reference range, especially if you have symptoms (e.g., headaches, visual changes, unusual itching), relevant exposures (smoking, high altitude), cardiopulmonary symptoms, or you’re using medications known to raise Hb/Hct (e.g., testosterone). [1,8]


When clinicians evaluate persistent erythrocytosis, commonly used tests may include repeat CBC, erythropoietin (EPO), and JAK2 testing (and sometimes additional tests based on clinical context). [1,2,3]

Final thoughts

A high hemoglobin result is a finding, not a diagnosis. Many causes are reversible or related to oxygen exposure, while a smaller subset reflects a primary blood disorder such as PV. If elevations are persistent, a clinician can use history, repeat testing, and focused labs (such as EPO and JAK2 when appropriate) to identify the cause and guide safe management. [1,2,3]

Abbreviation

PV — Polycythemia vera

Hb — Hemoglobin

CBC — Complete blood count

Hb/Hct — Hemoglobin / Hematocrit

Hct — Hematocrit

COPD — Chronic obstructive pulmonary disease

ESAs — Erythropoiesis-stimulating agents

P50 — P50 (oxygen dissociation measure)

EPO — Erythropoietin

JAK2 — Janus kinase

References

  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 IF: 11.3 Q1 B1
  2. IF: 11.3 Q1 B1
  3. Barbui, T., Thiele, J., Gisslinger, H., et al. (2018). The 2016 WHO classification and diagnostic criteria for myeloproliferative neoplasms: Document summary and in-depth discussion. Blood Cancer Journal, 8, 15. https://doi.org/10.1038/s41408-018-0054-y
  4. National Cancer Institute. (2024, September 27). Myeloproliferative neoplasms treatment (PDQ®)–Health professional version.
  5. Villafuerte, F. C., Simonson, T. S., Bermudez, D., & León-Velarde, F. (2022). High-Altitude Erythrocytosis: Mechanisms of Adaptive and Maladaptive Responses. Physiology (Bethesda), 37(4). https://doi.org/10.1152/physiol.00029.2021
  6. Rha, M. S., Kim, C. H., Yoon, I. Y., & Hong, S. C. (2022). Is obstructive sleep apnea associated with erythrocytosis? A systematic review and meta-analysis. Sleep Medicine Reviews, 62, 101593.
  7. Zeng, Z., Zhou, X., Li, J., et al. (2022). Obstructive sleep apnea is associated with an increased prevalence of polycythemia in COPD patients. International Journal of Chronic Obstructive Pulmonary Disease, 17, 1729–1739.
  8. Agbariah, N., Shalev, V., & Tzoran, I. (2022). Polycythemia secondary to shisha smoking in a middle-aged man: A case report. Cureus, 14(12), e32861.
  9. Cervi, A., Balitsky, A. K., & Khan, S. (2017). Testosterone use causing erythrocytosis. CMAJ, 189(41), E1286–E1288. https://doi.org/10.1503/cmaj.170673
  10. Manns, B. J., Tonelli, M., & Hemmelgarn, B. R. (2012). The new FDA labeling for ESA—Implications for patients and providers. Clinical Journal of the American Society of Nephrology, 7(2), 348–353.
  11. U.S. Food and Drug Administration. (2017, August 4). FDA drug safety communication: Modified dosing recommendations to improve the safe use of erythropoiesis-stimulating agents (ESAs) in chronic kidney disease.
  12. Percy, M. J., Butt, N. N., Crotty, G. M., et al. (2009). Identification of high oxygen affinity hemoglobin variants in the investigation of patients with erythrocytosis. Haematologica, 94(9), 1321–1322.
  13. McMullin, M. F., Mead, A. J., Ali, S., et al. (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
  14. Stuart, B. J., & Viera, A. J. (2004). Polycythemia vera. American Family Physician, 69(9), 2139–2144.
  15. Marchioli, R., Finazzi, G., Specchia, G., et al. (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