Increase in haemoglobin (Hb) and/or haematocrit (Hct) in peripheral blood.

• Relative (false) Polycythaemia: decreased plasma volume (hemoconcentration), RBC unchanged
• Absolute (true) Polycythaemia: increased RBCs
  • Primary: JAK mutation (either acquired or inherited) → myeloproliferation (Poly rubra vera)
  • Secondary: exogenous stimulation of erythropoiesis. Associated with elevated serum erythropoietin (EPO) which may be physiologically appropriate or inappropriate. *Remember EPO is produced in the kidneys and liver.

Aetiology

• Primary: JAK mutations → constant stim (myeloproliferative disorder: Poly rubra vera)
• Secondary (EPO driven)
  • Hypoxic state (heart disease, COPD, altitude, smoking (CO hogs Hb binding))
  • EPO secreting tumour (RCC, hepatoma)
  • Exogenous EPO (Lance Armstrong)
  • High O2 affinity Hb (fHb)
• Relative polycythaemia: dehydration (diarrhoea, vomiting, diuretics, excess alcohol)

Clinical Features

<aside> 💡 Overall: Increased RBC mass → Blood hyper-viscosity, vascular stasis and infarctions.

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• hyperviscocity symptoms (hypertension, dizziness, headaches, visual disturbances)
• Other symptoms depend on the underlying cause – i.e. clubbing in hypoxia, cardiac murmurs, renal or hepatic masses etc.

Investigation Findings

• FBC:
  • Hct: Increased (relative, primary and secondary polycythaemia).
  • Hb: Increased (relative, primary and secondary polycythaemia).
  • RBCs: Increased (primary and secondary polycythaemia).
  • WCC/Plts: Increased (primary polycythaemia), ? depends on underlying cause (secondary polycythaemia).
  • MCV: Nil changes (primary and secondary polycythaemia).
• Blood film: Normocytic, normochromic RBCs, +/- blasts.
• To identify the underlying cause: UECs, LFTs, ABG etc.