Effect of microcytosis on erythrocyte rheology

Abstract

The degree of rheological benefit arising from microcytosis in polycythaemia is controversial. The filterability (3 µm diameter pores) and viscosity (241 s^−l shear rate) of microcytic erythrocytes from 18 patients with polycythaemia were therefore compared with microcytes from 19 patients with iron deficiency and 12 patients with β-thalassaemia trait. In all three disorders, viscosity decreased as cell size decreased. Erythrocyte filterability was significantly impaired in polycythaemia compared with thalassaemia trait as a consequence of the greater degree of erythrocyte anisocytosis in polycythaemia. The beneficial rheological benefit of microcytosis is therefore reduced when the erythrocytes are not homogeneous in size and contain sub-populations of relatively large cells.