Polycythaemia

What is Polycythaemia?

Polycythaemia refers to an elevated haemoglobin (Hb) or haematocrit (Hct). It may be relative (due to dehydration) or absolute (due to increased red cell mass from primary or secondary causes).

Common Causes

  • Dehydration (relative polycythaemia)
  • Chronic hypoxia (e.g. COPD, obstructive sleep apnoea)
  • Smoking
  • Polycythaemia vera (myeloproliferative disorder)
  • High altitude exposure
  • Renal disease (e.g. EPO-producing tumours)
  • Exogenous erythropoietin use

Stepwise Clinical Approach

Step 1: Confirm and Repeat

Confirm persistent raised Hb and Hct on repeat testing to exclude lab or hydration artefact.

When repeating, also request:

  • Serum erythropoietin (EPO) level: to help differentiate primary vs secondary polycythaemia
  • JAK2 mutation testing: to screen for polycythaemia vera
  • Renal function tests: to assess for renal causes (e.g. cysts, tumours)
  • Oxygen saturation: to assess for hypoxic drive (e.g. COPD)
  • Chest X-ray: to assess for chronic lung disease

These tests help distinguish between primary bone marrow disorders and secondary reactive causes.

Step 2: Identify Reactive Causes

  • Recent dehydration, diuretic use, or diarrhoea?
  • Smoking or history of obstructive sleep apnoea?
  • Known chronic lung disease (e.g. COPD)?

If a secondary cause is likely, manage the underlying issue and repeat bloods after resolution.

Step 3: Interpretation Based on Investigations

  • Low EPO + JAK2 positive: polycythaemia vera likely
  • Raised EPO + hypoxia: secondary to chronic hypoxia
  • Raised EPO without hypoxia: search for EPO-producing tumours (e.g. renal)

Step 4: Monitor or Refer

  • Dehydration-related polycythaemia: rehydrate and reassess
  • Secondary causes (e.g. smoking, COPD): manage underlying condition and monitor
  • Confirmed or suspected polycythaemia vera: urgent referral to haematology

Step 5: Red Flags Requiring Urgent Action

  • Symptoms of hyperviscosity (e.g. headache, visual disturbance, dizziness)
  • Splenomegaly
  • Thrombosis (e.g. stroke, DVT) at young age or unprovoked
  • Very high Hb/Hct (e.g. Hct > 0.60)

Urgent haematology referral is indicated if red flags are present.

mypanotes