Polycythaemia/Erythrocytosis is abnormally high haematocrit and haemoglobin concentration

• Haematocrit is a more reliable indicator

Polycythaemia may be relative, primary (polycythaemia rubra vera) or secondary

Relative causes

Relative erythrocytosis is where the red cell volume is normal but there is a decrease in the plasma volume

• dehydration
• burns
• stress: Gaisbock syndrome: normal red cell volume, relative due to reduced plasma volume
• Most common in those taking diuretics, heavy smokers, heavy alcohol consumption

Primary

polycythaemia rubra vera

Secondary causes

increased red cell mass caused by an increased production of EPO, due to physiological responce to chronic tissue hypoxia caused by chronic lung disease (e.g. COPD)

• COPD
• altitude
• obstructive sleep apnoea
• excessive erythropoietin: cerebellar haemangioma, hypernephroma, hepatoma, uterine fibroids*