Whole blood viscosity in polycythaemia: the effect of iron deficiency at a range of haemoglobin and packed cell volumes.

The effect of iron deficient red cells changes (MCH range 20.0-32.6 pg) on whole blood viscosity (WBV) at high and low shear rates (94.5 and 0.51 s-1), has been assessed at a wide range of standardized PCV (0.30-0.65) and standardized Hb values (10.0-22.0 g/dl). Particular attention was given to the precision of PCV measurement. At all PCV values there was no correlation between MCH and WBV, whereas at all Hb values there was a significant negative correlation between MCH and WBV. If the treatment of polycythaemia is by venesection, iron deficient red cell changes occur frequently. These changes are unimportant if control of the WBV is the objective of treatment, as long as the PCV is accurately measured. Alternatively, in the secondary polycythaemias, where oxygen saturation is reduced, the induction of iron deficient red cell changes could be regarded as disadvantageous since at a standard PCV of 0.50 the Hb and hence oxygen carrying capacity is reduced by approximately 11% between MCH values of 30 and 20 pg.