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High Red Blood Cell Count Symptoms: What They Mean and When to Worry

Feb 7, 2026

Key takeaways

  • A “high red blood cell count” is a lab finding, usually interpreted together with hemoglobin/hematocrit and the overall clinical picture. [1,2]
  • Some people have no symptoms. When symptoms occur, they can include headache, dizziness, fatigue, skin redness, and visual changes—none are specific to one cause. [1,2]
  • Causes are often grouped as relative (less plasma), secondary (response to low oxygen/other drivers), or primary (polycythemia vera). [1,3,4]

Overview

Red blood cells carry oxygen from the lungs to the rest of the body. A “high RBC count” on a complete blood count (CBC) indicates more red cells than expected and is typically interpreted along with hemoglobin and hematocrit. [1,2]

An elevated red-cell concentration can be associated with higher blood viscosity in some settings and, depending on the cause—particularly in polycythemia vera (PV)—may contribute to a higher risk of thrombosis. [2,5]

Because a high RBC count is not a diagnosis by itself, the key is identifying whether the finding is persistent and what is driving it. [1,2]

Common symptoms of a high red blood cell count

Symptoms vary by the degree of elevation and the underlying cause. Some people have no symptoms. When symptoms occur, they may include: [1,2]

1. Headache, dizziness, or lightheadedness [1,2]

2. Fatigue (sometimes with reduced exercise tolerance) [1,2]

3. Skin redness or facial flushing [2,3]

4. Blurred vision or visual disturbances [2,3]

5. Tingling or burning sensations in the hands/feet [2,3]

6. Shortness of breath or chest discomfort (especially when an underlying cardiopulmonary condition or a clot-related complication is present) [1,2]

7. Itching after warm baths/showers (aquagenic pruritus), which is commonly reported in PV [6]


Note: These symptoms are nonspecific and should not be used to self-diagnose PV or any other condition. [1,2]

Causes of a high red blood cell count

Clinicians often group causes into three broad categories: [1,2]


1. Relative causes (less plasma volume)

Red-cell measures can appear high when plasma volume is reduced (for example, dehydration). [1,2]


2. Secondary causes (a response to another driver)

The body may increase red cell production in response to low oxygen or other stimuli. Examples include chronic lung disease, sleep-disordered breathing, high altitude exposure, and smoking. Some medications (including testosterone formulations) can also contribute. Kidney-related conditions may raise erythropoietin (EPO), a hormone that stimulates red cell production. [1,2, 4 ]


3. Primary cause — Polycythemia vera (PV)

PV is a myeloproliferative neoplasm characterized by overproduction of blood cells, most often associated with JAK2 variants, and evaluated using a combination of blood counts, molecular testing, and—when indicated—bone marrow findings and additional tests (including serum EPO). [2,3,4,7]

When to see a doctor

Contact a healthcare professional if a blood test shows elevated red-cell measures (especially hemoglobin/hematocrit) on repeat testing, or if you have new, persistent, or worsening symptoms such as headache, dizziness, marked itching after warm showers, unexplained redness, or visual changes. [1,2]


Seek urgent evaluation for possible clot-related warning signs (for example, sudden weakness on one side, difficulty speaking, sudden chest pain, or sudden severe shortness of breath).


How clinicians may evaluate a high result

Depending on your history and examination, clinicians may consider: [1,2]

    • Repeat CBC (to confirm persistence)
    • Oxygen assessment (to evaluate for hypoxic drivers)
    • Serum EPO level
    • JAK2 testing when PV is a concern
    • Additional testing (which may include bone marrow evaluation in selected cases)

Final thouhgts

A high red blood cell count is a lab finding that warrants clinical interpretation—often by confirming persistence and evaluating relative, secondary, and primary causes.


PV is an important primary cause assessed with blood counts plus molecular testing such as JAK2, with additional assessments as needed. With appropriate evaluation and cause-directed management, many people can be treated effectively and monitored safely. [1,2,3]

Abbreviation

RBC — Red blood cell

CBC — Complete blood count

PV — Polycythemia vera

EPO — Erythropoietin

JAK2 — Janus kinase 2

References

  1. Mithoowani, S., Laureano, M., Crowther, M. A., & Hillis, C. M. (2020). Investigation and management of erythrocytosis. CMAJ, 192(32), E913–E918.
  2. Gangat, N., & Tefferi, A. (2021). JAK2 unmutated erythrocytosis: Current diagnostic approach and therapeutic views. Leukemia.
  3. 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.
  4. McMullin, M. F., Harrison, C. N., Ali, S., et al. (2019). A guideline for the management of specific situations in polycythaemia vera and secondary erythrocytosis: A British Society for Haematology Guideline. British Journal of Haematology, 184(2), 161–175.
  5. 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.
  6. Siegel, F. P., Tauscher, J., & Petrides, P. E. (2013). Aquagenic pruritus in polycythemia vera: Characteristics and influence on quality of life in 441 patients. American Journal of Hematology, 88(8), 665–669.
  7. Arber, D. A., Orazi, A., Hasserjian, R. P., et al. (2022). International Consensus Classification of myeloid neoplasms and acute leukemias: Integrating morphologic, clinical, and genomic data. Blood, 140(11), 1200–1228.