Classification

Polycthaemia may be ‘relative’ or ‘absolute’.

In relative polycythaemia, the plasma volume is reduced. Relative polycythemia is often due to dehydration.

Absolute polycythaemia can be primary or secondary

Primary polycythaemia is known as polycythaemia rubro vera

Secondary polycythaemia may be due to high altitude, chronic lung disease and some tumours.