Viscosity and iron deficiency in treated polycythaemia.

An in vitro study of the effect of red-cell changes due to iron deficiency on whole-blood viscosity has been made on samples from patients with polycythaemia treated by venesection. When the PCV of the samples was adjusted to a standard value of 0.45, whole-blood viscosity was unrelated to decreasing MCH. In contrast, when samples were adjusted to a standard Hb concentration of 14 g/dl, whole-blood viscosity rose exponentially with decreasing MCH. This increase in whole-blood viscosity was shown to be a function of the increasing PCV that accompanies the falling MCH at this standard Hb value. It is suggested that in polycythaemia not due to hypoxia, hyperviscosity can be satisfactorily corrected by venesection controlled by monitoring the PCV alone. Other consideration may apply in hypoxic polycythaemia and these are discussed.