  The deformability of human red blood cells (RBCs), which comprise almost 99%
of the cells in whole blood, is largely related not only to pathophysiological
blood flow but also to the levels of intracellular compounds. Therefore,
statistical estimates of the deformability of individual RBCs are of paramount
importance in the clinical diagnosis of blood diseases. Although the
micro-scale hydrodynamic interactions of individual RBCs lead to non-Newtonian
blood rheology, there is no established method to estimate individual RBC
deformability from the rheological data of RBC suspensions, and the possibility
of this estimation has not been proven. To address this issue, we conducted an
integrated analysis of a model of the rheology of RBC suspensions, coupled with
macro-rheological data of human RBCs suspended in plasma. Assuming a non-linear
curve of the relative viscosity of the suspensions as a function of the cell
volume fraction, the statistical average of the membrane shear elasticity was
estimated for individual intact RBCs or hardened RBCs. Both estimated values
reproduced well the experimentally observed shear-thinning non-Newtonian
behavior in these suspensions. We hereby conclude that our complementary
approach makes it possible to estimate the statistical average of individual
RBC deformability from macro-rheological data obtained with usual rheometric
tests.
