In polycythaemia rubra vera, as with all myeloproliferative disorders, there are excess granulocytic, and megakaryocytic elements, all derived from a single multipotent stem cell.

However, in polycythaemia vera the erythroid precursors dominate, and hence there is an absolute increase in red cell mass and blood volume. In polycythaemia rubra vera the erythroid offspring are unusual in being sensitive eg to insulin-like growth factor ± interlukin-3 - they are also do not require erythropoietin to avoid apoptosis (programmed cell death).

Polycythaemia rubra vera has an incidence of 1.5/100,000/year.

The incidence peaks at 45-60yrs old.