Rheological properties of antibody-coated red cells

In vivo and in vitro antibody-coated nonspherocytic red cells have normal deformability in iso-osmolar media, and their isolated membranes have normal mechanical stability as measured in the ektacytometer, a laser visco-diffractometer. The deformability of red cells from patients with hemolytic anemia was proportionately reduced with the degree of spherocytosis irrespective of whether the direct antiglobulin test was positive. However, when antibody-sensitized nonspherocytic cells were suspended in hyperosmolar media and exposed to constant shear stress in the ektacytometer, they showed reduction of their deformability index in the presence of polyvinylpyrrolidone (PVP; 360,000 Daltons) but not dextran. This reduction was not due to alterations in cell water or cation content. Also, when incubated at 37 degrees C, sensitized red cells reacted specifically with PVP, and underwent a decrease in cell deformability. This appears to be the result of changes either in red cell membrane rigidity or membrane viscosity. The PVP effect was reproducible, time- and temperature-dependent, and predicted reliably the Rh phenotype. These observations were used to develop a novel approach to the antiglobulin test in the blood bank.