Polycythaemia

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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.

Who gets 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.

Predisposing Factors

Secondary polycythaemia is due to:

An increase in red blood cells in response to anoxia (lack of oxygen): high altitude, lung disease, heart diease, heavy smoking;

or 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

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.

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