Clinical Review

ABC of clinical haematology: Polycythaemia, primary (essential) thrombocythaemia and myelofibrosis

BMJ 1997; 314 doi: (Published 22 February 1997) Cite this as: BMJ 1997;314:587
  1. Maria Messinezy,
  2. T C Pearson

    Primary polycythaemia (polycythaemia rubra vera), primary (or essential) thrombocythaemia, and myelofibrosis are all clonal disorders originating from a single aberrant neoplastic stem cell in the bone marrow. They are generally diseases of middle or older age and have or may develop common features including a small potential for transforming to acute leukaemia. Myelofibrosis may arise de novo or result from progression of primary polycythaemia or primary thrombocythaemia. Treatment of primary polycythaemia and primary thrombocythaemia can greatly influence prognosis, hence the importance of diagnosing these rare disorders. They need to be distinguished from other types of polycythaemia (secondary polycythaemia, apparent polycythaemia) and other causes of a raised platelet count (secondary or reactive thrombocytosis), whose prognosis is different.


    The packed cell volume, rather than the haemoglobin concentration, is the indicator of polycythaemia. A raised packed cell volume (> 0.51 in males, > 0.48 in females) needs to be confirmed on a specimen taken without venous occlusion. Patients with a persistently raised packed cell volume should be referred to a haematologist for measurement of red cell mass by radionuclide labelling of the red cells. Red cell mass is best expressed as the percentage difference between the measured value and that predicted from the patient's height and weight (derived from tables).

    Symptoms and signs of primary polycythaemia

    • Stroke

    • Transient ischaemic attack

    • Digital ischaemia

    • Headache

    • Mental clouding

    • Facial plethora

    • Pruritus

    • Bleeding (including gastrointestinal tract)

    • Gout

    Red cell mass more than 25% above the predicted value constitutes real or absolute polycythaemia, of which there are two types: primary and secondary. When the packed cell volume is raised but the red cell mass is not, the condition is known as apparent polycythaemia.

    Palpable splenomegaly is present in less than half of patients with primary polycythaemia, but when present it reliably distinguishes primary polycythaemia from the other polycythaemias

    Classification of the polycythaemias.

    Primary polycythaemia

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