Mean corpuscular hemoglobin concentration and cell deformability.

A prominent characteristic of sickle cells is the presence of a subpopulation of severely dehydrated cells. Apart from its effect on the rate and extent of Hb S polymerization at low oxygen tension, dehydration has adverse effects on deformability of oxygenated sickle cells. In general, the degree of deformability defect induced by cellular dehydration measured in vitro depends on the method used to measure deformability. Methods in which the extent or rate of cellular deformation are measured are especially sensitive to intracellular Hb concentration, whereas filtration methods are more sensitive to cell size. Studies of naturally occurring cellular dehydration in red cell disorders other than sickle cell disease have indicated that red cells can tolerate dehydration and a substantial increase in intracellular viscosity much more readily than a loss of deformability that results from loss of surface area or increase in cell volume. Further, the major clinical problems in sickle cell disease, involving occlusion of small vessels, do not correlate with the proportion of poorly deformable, dehydrated cells. Thus, the direct rheologic effects of cellular dehydration in sickle cell disease are probably much less important than the effects of MCHC on the kinetics of Hb S polymerization.