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Relative Polycythemia: When Blood Appears Thick Without True OverproductionShape

Feb 9, 2026

Key takeaways

  • Relative polycythemia (also called relative erythrocytosis, spurious polycythemia, or sometimes stress polycythemia/Gaisböck syndrome) is not caused by increased red cell; it reflects reduced plasma (liquid) volume with a normal red cell mass. [1][2]
  • It can occur with dehydration and may be described in some contexts alongside hypertension / obesity / stress patterns. [2][3]
  • Unlike polycythemia vera, relative polycythemia does not reflect bone-marrow overproduction; PV is a myeloproliferative neoplasm typically associated with acquired JAK2 variants. [4][5]

Overview

Relative polycythemia is a condition where blood tests show an apparently high hematocrit (the percentage of red blood cells in the blood), but the total red blood cells remains within the normal range. This happens because the liquid portion of blood, called plasma, is reduced, concentrating the existing red cells and making the sample appear “thicker,” even though there is no true overproduction of red blood cells. [1][2]


This condition is sometimes referred to as spurious polycythemia and, in certain clinical contexts, stress polycythemia/Gaisböck syndrome, historically described in patients with hypertension and a plethoric appearance without splenomegaly, thought to reflect a form of relative erythrocytosis. [3][6]

Causes of Relative Polycythemia

Relative polycythemia is due to plasma volume loss rather than excessive red blood cell production. Common causes include:

  1. Dehydration, including gastrointestinal fluid losses (vomiting/diarrhea) or reduced intake. [2]
  2. Diuretic use, which can reduce plasma volume and concentrate blood values. [2][6]
  3. Stress polycythemia (Gaisböck syndrome), a label used for relative erythrocytosis patterns described in association with hypertension and often obesity/stress features. [3][6]


In these situations, the hematocrit may be elevated because the plasma fraction is lower, while red cell mass is not truly increased. [1][2]

Symptoms

Symptoms are usually mild and may relate to hemoconcentration and coexisting factors (e.g., dehydration, hypertension). They may include:

  • Headache or dizziness
  • Facial redness or a flushed appearance
  • Fatigue
  • Mild hypertension
  • Anxiety or tension-related symptoms


These symptoms often improve once the trigger (such as dehydration or medication-related volume contraction) is addressed. [2][6]

How does it differ from true polycythemia (Polycythemia Vera)?

Relative polycythemia must be distinguished from polycythemia vera (PV), a chronic myeloproliferative neoplasm characterized by increased red blood cell mass and typically an acquired JAK2 variant. [4][5]


Feature

Relative Polycythemia

Polycythemia Vera (PV)

Red Cell Mass

Normal

Increased

Plasma Volume

Decreased

Normal or slightly low

JAK2 Mutation

Absent

Present in >95% of patients [4]

Bone Marrow Activity

Not overactive

Overactive

Common Drivers

Dehydration, diuretics; sometimes labeled “stress/Gaisböck” patterns

Clonal myeloproliferation (JAK2-driven in most cases

Diagnosis

To confirm relative polycythemia, clinicians first confirm that the elevation is persistent and then evaluate for relative vs absolute causes of erythrocytosis. A key concept is that relative erythrocytosis reflects reduced plasma volume with normal red cell mass. [1][2]


In practice, workup commonly includes:

  • Repeating CBC after addressing possible dehydration/volume contraction and reviewing medications (including diuretics). [2][6]
  • Evaluating for secondary causes of erythrocytosis (history/physical; oxygenation and exposure review as appropriate). [2][5]
  • JAK2 testing when PV is in the differential, because PV is typically JAK2-associated and is managed differently. [4][5]

Treatment

Treatment for relative polycythemia focuses on correcting factors that reduce plasma volume (e.g., dehydration or diuretic-related volume contraction) and managing associated contributors (such as hypertension/obesity in “stress/Gaisböck” presentations), rather than using PV-directed therapies. [1][7][8]

Final Thoughts

Relative polycythemia is is typically a reversible form of hemoconcentration caused by reduced plasma volume rather than true red cell overproduction. Recognizing the distinction from PV is important because management focuses on hydration/volume status and risk-factor control—not PV-directed therapy. [2][4]

Frequently Asked Questions (FAQs)

1. Is relative polycythemia dangerous?

Usually not, but it’s important to identify and correct the cause (e.g., dehydration, medication-related volume contraction) and manage coexisting risk factors (like hypertension) when present. [2][6]


2. How can doctors tell if it’s relative or true polycythemia?

They evaluate whether findings fit relative erythrocytosis (plasma volume reduction) versus absolute erythrocytosis, and they may use targeted testing (including JAK2 testing when PV is considered). [1][2]


3. Can stress alone cause polycythemia?

“Stress polycythemia/Gaisböck syndrome” is a term used for relative erythrocytosis patterns historically associated with hypertension and a plethoric appearance, with stress sometimes proposed as a contributor. [3][6]


4. Do I need treatment for relative polycythemia?

Often, no PV-directed therapy is needed; treatment focuses on correcting the underlying driver. [2][6]


5. Can relative polycythemia turn into polycythemia vera?

They are distinct entities: relative polycythemia reflects hemoconcentration, while PV is a clonal myeloproliferative neoplasm (typically JAK2-associated). [2][4]

Abbreviation

PV — Polycythemia vera

JAK2 — Janus kinase 2

CBC — Complete blood count

FAQs — Frequently asked questions


References

  1. Noumani, I., Harrison, C. N., & McMullin, M. F. (2024). Erythrocytosis: Diagnosis and investigation. International Journal of Laboratory Hematology, 46(Suppl 1), 55–62. https://doi.org/10.1111/ijlh.14298
  2. 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
  3. Evans, A., Songtanin, B., & Nugent, K. (2022). The Gaisbock syndrome after COVID-19 pneumonia. Proceedings (Baylor University. Medical Center), 35(2), 207–208. https://doi.org/10.1080/08998280.2021.2022370
  4. Tremblay, D., Kremyanskaya, M., Mascarenhas, J., & Hoffman, R. (2025). Diagnosis and treatment of polycythemia vera: A review. JAMA, 333(2), 153–160. https://doi.org/10.1001/jama.2024.20377
  5. McMullin, M. F., Mead, A. J., Ali, S., et al. (2019). A guideline for the diagnosis and management of polycythaemia vera. British Journal of Haematology, 184(2), 176–191. https://doi.org/10.1111/bjh.15648
  6. Haider, M. Z., & Anwer, F. (2023). Polycythemia. In StatPearls [Internet]. StatPearls Publishing. Retrieved February 3, 2026, from https://www.ncbi.nlm.nih.gov/books/NBK526081/
  7. 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
  8. Manal, N., Rizvi, M., & Nugent, K. (2023). Gaisbock syndrome: A review of contemporary studies, pathogenesis, complications, and possible treatment. Cardiology in Review, 31(5), 247–251. https://doi.org/10.1097/CRD.0000000000000443