Red face and reduced plasma volume.

Twenty-five patients who were suspected clinically of having either polycythaemia rubra vera or secondary polycythaemia had no haematological abnormalities apart from a reduction in the plasma volume. Twenty-one were hypertensive. The plasma volume was lowest in those who were receiving treatment with diuretic agents, antihypertensive drugs, or steroid therapy. These cases demonstrate the need for blood volume studies in patients with high values for the blood haemoglobin and the packed cell volume in order to establish a differential diagnosis from myeloproliferative disorder or secondary polycythaemia.