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Test Findings


June 6th, 2021


Erythrocytosis is the presence of increased circulating red blood cells.
The terms erythrocytosis and polycythaemia are often used interchangeably, though polycythaemia is less specific as it suggests pathology in multiple cell lineages.
  • Look For

  • Increased red cell count (RCC)
  • Elevated haemoglobin (Hb)
  • Elevated haematocrit (HCT) / packed cell volume (PCV)
  • Interpretation

  • Elevated Hb / PCV with elevated RCC - absolute erythrocytosisBone marrow pathology (primary) or excess erythropoietin (secondary)
  • Elevated Hb / PCV with normal RCC - relative erythrocytosisContraction of plasma volume
  • Causes of Erythrocytosis

  • Primary

  • Primary familial erythrocytosis (EPO receptor mutation)
  • Polycythaemia vera (JAK2 mutation)
  • Secondary

  • Chronic hypoxia - smoking, chronic lung disease, obstructive sleep apnoea, high altitude
  • Renal hypoxia - renal artery stenosis, polycystic kidney disease, post renal transplant
  • Drugs - testosterone, anabolic steroids, erythropoietin
  • Paraneoplastic syndrome (EPO-producing tumour)
  • Congenital - haemoglobinopathies, other mutations
  • Idiopathic
  • Relative

  • Severe dehydration
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