The term polycythaemia has traditionally been used to described disorders in which there is an increase in the number of red cells resulting in a persistently raised haematocrit. However, since usually only red cells are involved erythrocytosis is a more accurate term, and polycythaemia should really be reserved for polycythaemia vera which involves 3 cell lineages.

Erythrocytosis is defined as a raised haematocrit >0.52 in men or >0.48 in women for >2 months

It may be subdivided into
  • primary polycythaemia (=polycythaemia rubra vera)
  • secondary erythrocytosis
  • apparent erythrocytosis

The initial investigations on a finding of erythrocytosis should be
  • History and examination
  • FBC and blood film
  • JAK2 mutation
  • Serum ferritin
  • U&Es and LFTs

If the JAK2 is negative and there is no obvious secondary cause the next line of investigations should be:
  • Red cell mass
  • Arterial oxygen saturation
  • Abdominal ultrasound
  • Serum erythropoietin level
  • Bone marrow aspirate and trephine
  • Cytogenetic analysis
  • BFU-E culture

Primary polycythaemia

  • Presentation
    • Thrombosis
    • Pruritus after baths
    • Burning pain in distal extremities
    • Splenomegaly
    • Weight loss
    • Sweating
    • Plethora
    • Haemorrhagic events
    • Gout

  • Diagnostic criteria are:
    • If JAK2 positive (= around 95%)
      • High haematocrit (>0.52 in men, >0.48 in women) OR raised red cell mass (>25% above predicted)
    • If JAK2 negative
      • Raised haematocrit >0.60 in men or 0.56 in women OR raised red cell mass >25% above predicted AND
      • No cause of secondary erythrocytosis
      • Then either
        • Palpable splenomegaly OR
        • presence of an acquired genetic abnormality (excluding BCR-ABL) in the haematopoietic cells OR
        • 2 of
          • Thrombocytosis (platelet count >450x10^9/l)
          • Neutrophil leukocytosis (neutrophil count > 10 x10^9/l in non-smokers or 12.5x10^9/l in smokers
          • Radiological evidence of splenomegaly
          • Endogenous erythroid colonies or low serum erythropoietin

  • Management
    • Venesection – maintain haematocrit at less than 0.45
    • Aspirin 75mg od unless contraindicated
    • Cytoreduction (interferon or hydroxycarbamide = hydroxyurea) should be considered if
      • Venesection isn’t tolerated
      • Symptomatic or progressive splenomegaly
      • Thrombocytosis
      • Evidence of disease progression, eg weight loss, night sweats

Secondary erythrocytosis

  • Causes
    • Hypoxia
      • COPD
      • High altitude
      • Cyanotic congenital heart disease
    • Renal pathology
    • Erythropoietin-secreting tumours

Apparent erythrocytosis

  • Apparent erythrocytosis is defined as raised haematocrit but normal red cell mass.

  • Possible causes for apparent erythrocytosis include:
    • Physiological variant
    • Obesity
    • Smoking
    • Alcohol
    • Renal disease
    • Hypertension
    • Diuretics

  • If the apparent erythrocytosis is due to decreased plasma volume (ie dehydration) it is called relative erythrocytosis.

  • Management
    • Reduction of risk factors
    • Consider venesection if
      • Recent history of thrombosis or risk factors for thrombosis
      • Haematocrit >0.54

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