What are the causes of increased hemoglobin (polycythemia)?

Medical Advisory BoardAll articles are reviewed for accuracy by our Medical Advisory Board
Educational purpose only • Exercise caution as content is pending human review
Article Review Status
Submitted
Under Review
Approved

Last updated: October 14, 2026 • View editorial policy

Have a follow-up question?

Our Medical A.I. is used by practicing medical doctors at top research institutions around the world. Ask any follow up question and get world-class guideline-backed answers instantly.

Ask Question

Causes of Increased Hemoglobin (Polycythemia)

Increased hemoglobin results from either true polycythemia (polycythemia vera or secondary causes) or apparent polycythemia (relative polycythemia from plasma volume contraction), with the most critical distinction being between the primary clonal disorder polycythemia vera and secondary causes driven by hypoxia or inappropriate erythropoietin production.

Classification Framework

Polycythemia divides into two major categories 1:

Apparent Polycythemia (Not True Increase in Red Cell Mass)

  • Relative polycythemia: Plasma volume contraction from dehydration, severe vomiting, diarrhea, diuretic use, capillary leak syndrome, or severe burns 1
  • Extreme "high-normal" values: Hemoglobin/hematocrit at the upper end of the 95th percentile that exceeds 2 SD from mean but represents normal variation 1

Clinical Pearl: Gaisböck syndrome and "stress polycythemia" lack solid evidence—Mayo Clinic data found zero cases of true relative polycythemia in 109 consecutive measurements 1. Smoker's polycythemia, however, is real and resolves with smoking cessation 1.

True Polycythemia (Actual Increase in Red Cell Mass)

Primary: Polycythemia Vera

  • Clonal myeloproliferative neoplasm caused by JAK2 mutations (V617F or exon 12) 2, 3
  • Autonomous red cell proliferation independent of erythropoietin
  • Diagnostic criteria: Hemoglobin ≥18.5 g/dL (men) or ≥16.5 g/dL (women) PLUS JAK2 mutation 2
  • Low serum erythropoietin levels 1
  • Often accompanied by leukocytosis, thrombocytosis, and splenomegaly 4, 5

Secondary Polycythemia: EPO-Mediated, Hypoxia-Driven

Central hypoxic processes 1:

  • Chronic lung disease (COPD most common) 5
  • Right-to-left cardiopulmonary shunts
  • High-altitude habitation
  • Carbon monoxide poisoning/chronic exposure (smoker's polycythemia)
  • Hypoventilation syndromes including obstructive sleep apnea 5

Peripheral hypoxic processes 1:

  • Localized: Renal artery stenosis
  • Diffuse:
    • High oxygen-affinity hemoglobinopathies (congenital, autosomal-dominant)
    • 2,3-Diphosphoglycerate mutase deficiency (congenital, autosomal-recessive)

Secondary Polycythemia: Hypoxia-Independent EPO Production

Malignant tumors producing pathologic EPO 1:

  • Hepatocellular carcinoma
  • Renal cell cancer
  • Cerebellar hemangioblastoma
  • Parathyroid carcinoma

Nonmalignant conditions 1:

  • Uterine leiomyomas
  • Renal cysts (polycystic kidney disease)
  • Pheochromocytoma
  • Meningioma

Congenital causes 1:

  • Chuvash polycythemia (von Hippel-Lindau gene mutation, abnormal oxygen homeostasis)
  • Abnormally elevated set point for EPO production

Secondary Polycythemia: EPO Receptor-Mediated

  • Activating mutations of the EPO receptor (EPOR) gene 1
  • Results in C-terminal-truncated receptor with enhanced signal transduction
  • Seen in some autosomal-dominant congenital polycythemia cases
  • Serum EPO typically low in these patients 1

Drug-Associated Secondary Polycythemia

  • Exogenous EPO administration (EPO doping) 1
  • Androgen preparations 1
  • SGLT2 inhibitors 4

Unknown Mechanisms

  • Most cases of autosomal-dominant congenital polycythemia 1
  • Some autosomal-recessive congenital polycythemia
  • Post-renal transplant erythrocytosis (PRTE)—may involve EPO hypersensitivity or increased IGF-1 1

Diagnostic Approach Algorithm

When polycythemia is isolated (no leukocytosis/thrombocytosis) 4:

  1. First exclude secondary and hereditary causes
  2. Measure serum EPO levels
  3. Evaluate for hypoxic conditions and tumors

When polycythemia accompanies leukocytosis or thrombocytosis 4:

  1. Test for JAK2 mutations immediately
  2. Measure serum EPO levels
  3. Consider bone marrow biopsy if JAK2 positive

Critical Caveats

  • Iron deficiency masks polycythemia vera: Hemoglobin may fall into normal range despite underlying PV 2. In clinical practice, make a working diagnosis of PV despite not meeting WHO criteria if JAK2 mutation present with iron deficiency.

  • Hypoxia can coexist with PV: A patient may have both polycythemia vera and chronic lung disease 1.

  • Thrombotic risk: Polycythemia vera patients are significantly more symptomatic with higher thrombotic tendency (arterial > venous) compared to secondary polycythemia 5. Leukocytosis and JAK2 positivity predict higher thrombotic risk 5.

  • EPO levels fluctuate: In hypoxia-driven secondary polycythemia, EPO may initially be elevated but return to normal once hemoglobin stabilizes 1.

References

Related Questions

Which type of physician treats polycythemia and thalassemia?
In a patient with flu‑like symptoms, cough, and undocumented fever and chills who has an elevated hemoglobin and hematocrit, what is the most likely etiology and appropriate management?
Which blood test should be performed to exclude polycythemia vera?
Can polycythemia vera cause an elevated high‑sensitivity C‑reactive protein (hs‑CRP) level in a 54‑year‑old woman?
Does polycythemia vera present with thrombocytopenia, leukopenia, macrocytosis, and pruritic ecchymoses on the arms?
Can I give lorazepam as a PRN for persistent agitation in a patient receiving haloperidol?
What are the recorded incidences of side effects of ursodeoxycholic acid (ursodiol)?
Can gabapentin cause urinary incontinence?
Does continuous renal replacement therapy cause coagulopathy?
What are the possible causes of an elevated C‑reactive protein with a normal erythrocyte sedimentation rate, negative fecal calprotectin, negative celiac serology, normal routine labs, and a normal abdominal‑pelvic computed tomography scan?
Can the patient who received a ketorolac (Toradol) injection today be continued on oral ketorolac (Toradol) and what is the appropriate dosing?

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.