Filterability and other methods of approaching red cell deformability. Determinants of blood viscosity and red cell deformability.

The major determinants of blood viscosity are RBC concentration, plasma viscosity, RBC aggregation and RBC deformation. RBC deformation is determined by the intrinsic deformability of the cell and the shear stress acting on the cell surface. In using filterability tests to assess RBC deformability, it is necessary to eliminate variations in other determinants of blood viscosity and to specify the rheological conditions of the test. Further theoretical and experimental work is needed for the interpretation of filterability tests in terms of cell geometry, internal viscosity and membrane properties.