Study of red blood cell aggregation by admittance measurements

A method based on dielectric properties of cellular suspensions was developed to study red blood cell (RBC) aggregability. The time-dependent current in a Couette-type viscometer was recorded after abrupt stoppage of shearing. Since the current reaches steady state 2 min after the end of shearing, the observed effects were quantified by the relative current difference, delta Irel = (I(2min)-I5s)/I2min, where subscripts designate the time of measurements. delta Irel increases with hematocrit, plasma and fibrinogen concentration. The dependence of delta Irel and of RBC aggregability on the concentration of dextran were similar. The experimental data and their analysis indicate that in suspensions with aggregating media, the delta Irel value measured in the field of the beta-dispersion reflects the difference between the size of aggregates under steady-state conditions and that of dispersed particles 5 s after the end of shearing. Therefore, this value may serve as a measure of RBC aggregability.