Polycythemia

Basics

Description

  • Increase in hemoglobin (Hgb) concentration and/or hematocrit (Hct) above the normal range
    • Diagnostic criteria derived from 2022 WHO classification and International Consensus Classification:
      • Men: Hgb >16.5 g/dL, Hct > 49%
      • Women: Hgb >16.0 g/dL, Hct > 48%
    • Other criteria include considerations of bone marrow biopsy and genetic mutations; these criteria are less useful in the ED setting
  • Classified as absolute (increased red cell mass [RCM]) or relative (decreased plasma volume but RCM remains normal)
    • Also classified as primary or secondary

Etiology

  • Relative (apparent) polycythemia:
    • Decreased plasma volume with normal RCM
    • Acute: Dehydration
    • Chronic: Gaisböck syndrome (“stress” polycythemia); idiopathic polycythemia seen in hypertension, nocturnal hypoxemia, or chronic tobacco or alcohol use
  • Primary erythrocytosis:
    • Polycythemia vera (PV): A myeloproliferative disorder characterized by overproduction of RBCs, WBCs, and platelets. Erythrocytosis is the most prominent feature:
      • Mutation in JAK2-STAT pathway
      • Median age 60
      • Male predominance
      • Highest incidence in Ashkenazi Jews
      • Median survival with treatment is 14 yr
      • May progress to myelofibrosis or acute leukemia
  • Secondary polycythemia:
    • Central hypoxia increasing erythropoietin (EPO):
      • Chronic pulmonary disease
      • Obstructive sleep apnea
      • Obesity hypoventilation syndrome (formerly Pickwickian syndrome)
      • Right-to-left cardiopulmonary shunt
      • High altitude (chronic)
      • Smoking
      • Carbon monoxide poisoning (chronic)
      • Chronic methemoglobinemia
    • Local renal hypoxia increasing EPO:
      • Renal cell carcinoma
      • Renal artery stenosis
      • Postrenal transplant
      • End-stage renal disease
      • Renal cysts
    • Inappropriate autonomous EPO production:
      • Multiple malignancies
    • Exogenous sources:
      • Recombinant EPO abuse
      • Autologous transfusions
      • Androgenic steroids
      • Testosterone
      • Antidiabetic agents (eg, SGLT2 inhibitors, such as canagliflozin)
  • Genetic disorders with polycythemia:
    • Primary hereditary disorders are very rare; involve mutation in EPO receptor gene
    • Secondary hereditary disorders are also rare; can involve gain-of-function mutations, among others

Diagnostic Criteria

  • Major criteria:
    • Hgb >16.5 g/dL in men, >16.0 g/dL in women
    • Bone marrow biopsy demonstrating hypercellularity with trilineage proliferation
    • Presence of JAK2 mutation
  • Minor criteria:
    • Low serum EPO level

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