What is Polycythaemia

Polycythaemia is defined as increase in haemoglobin, packed cell volume (PCV), and red cell count. A Hb > 170g/L in men or 150g/L in women or a PCV (haematocrit) >0.5 in men or >0.45 in women is highly suggestive of polycythaemia. Haemoglobin and packed cell volume reflect the concentration of red cells in the blood – hence they can be relatively high in dehydration. However, an absolute increase in red cell mass is true polycythaemia, or absolute erythrocytosis.

True polycythaemia itself can be either primary, or secondary. Secondary causes cause polycythaemia either by causing hypoxia (and hence stimulation to increase red cell production) or by increasing levels of erythropoietin (the hormone stimulating red cell synthesis) – eg certain tumours.

Primary polycythaemia is called Polycythaemia rubra vera, or just polycythaemia vera. It is a type of bone marrow malignancy.

Statistics on Polycythaemia

Secondary polycythaemia is common, due to the large number of conditions that can cause it.

Primary polycythaemia (PV) occurs in 2 per 100,000 people. It is more common in men in the older age group, and more commoin in women in the reproductive ages. PV tends to occur in patients aged over 60 years of age.

Risk Factors for Polycythaemia

Secondary polycythaemia is due to:

  • An increase in red blood cells in response to anoxia (lack of oxygen):
  • abnormal production of erythropoeitin (EPO):
    • renal cell carcinoma,
    • Wilms’ tumour,
    • hepatocellular carcinoma,
    • adrenal tumour

Primary polycythaemia, which is from bone marrow disease, is called polycythaemia rubra vera or just polycythaemia vera (PV). In PV there is an alteration in a bone marrow stem cell leading to excessive proliferation of blood cell precursors – the cells that give rise to red blood cells, as well as white blood cells and platelets.

Progression of Polycythaemia

Symptoms occur initially due to the increased red blood cell mass. Serious complications may develop due to abnormal blood flow (due to sluggish blood flow with increased viscosity), leading to thrombosis (clotting) and even haemorrhage. Progression to other bone marrow disorders such as myelofibrosis and acute myeloblastic leukaemia may occur.

How is Polycythaemia Diagnosed?

Full blood count – haemoglobin and packed cell volume (PCV) are increased (but this does not necessarily mean true polycythaemia). A Hb > 170g/L in men or 150g/L in women should be a cause of concern. Similarly a PCV (haematocrit) >0.5 in men or >0.45 in women is concerning. A PCV > 0.6 in men or >0.55 in women is however almost invariably associated with an increased red cell mass. White cell count is increased in 70% of cases, and platelet count is elevated in 50%. Serum uric acid may be raised.

Prognosis of Polycythaemia

In patients who receive no treatment, death occurs within months after diagnosis, due to bleeding or thrombosis. With treatment, however, median survivial of 10 years is achieved. PV progresses to myelofibrosis in 30% of cases and into AML in 5% – and these disorders have worse prognosis.

How is Polycythaemia Treated?

Treatment is aimed at keeping PCV below 0.45L/L and platelet count below 400 *10exp9/L) There are three types of treatment:

  • Venesection – this involves regular removal of blood, in the same way as blood donation (through a needle in an arm vein). It will successfully relieve many symptoms, and is often used as the sole treatment.
  • Chemotherapy– is used to control thrombocytosis (high platelets)
  • Radioactive 32P – one dose may control for 18 months, but this therapy carries an increased risk of transformation to acute leukaemia. It is confined to those over 70 years of age.

Allopurinol is also given to prevent gout. Itching is lessened by avoiding very hot baths. PV places patients at high risk of bleeding following surgery and the illness should be controlled before surgery.

Polycythaemia References

  1. Braunwald, Fauci, Kasper, Hauser, Longo, Jameson. Harrison’s Principles of Internal Medicine. 15th Edition. McGraw-Hill. 2001
  2. Cotran RS, Kumar V, Collins T. Robbins Pathological Basis of Disease Sixth Ed. WB Saunders Company 1999.
  3. Kumar P, Clark M. Clinical Medicine. Fourth Ed. WB Saunders, 1998.
  4. Talley NJ, O’Connor S. Clinical examination. Third Ed. MacClennan & Petty, 1996.

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