Polycythaemia

Polycythaemia is an increase in red cell concentration above the normal limit, usually accompanied by a corresponding increase in haematocrit and haemoglobin concentration. Polycythaemia can be ‘real’ due to a true increase in red cell concentration or ‘apparent’ due to low plasma volume (e.g. dehydration). Primary polycythaemia (polycythaemia vera) is due to a neoplasm of the myeloid cells whilst secondary polycythaemia is due to raised erythropoietin levels. This may be caused by chronic low oxygenation or erythropoietin production from renal tumours.