Comparison of light-transmission and -backscattering methods in the measurement of red blood cell aggregation.

Light-transmission and light-backscattering methods are commonly used to determine red-blood-cell (RBC) aggregation. Even though the results reveal good correlations between the parameters that are measured by these two methods, the methods themselves yield quite different values. The objective of this research is to investigate and delineate the characteristics of the two optical methods. We measured RBC aggregation by using a newly developed microchip-based aggregometer. An orthogonal polarization technique, wherein multiple scattering causes polarized light to be depolarized and passed through an orthogonal polarizer, was applied to the backscattering method. Our results were also compared to those of conventional aggregometers [laser-assisted optical rotational cell analyzer (LORCA)], and revealed that the backscattering method yielded higher aggregation indices than the transmission method and LORCA. However, the backscattering method with orthogonal polarization yielded the same values of aggregation indices as the transmission method. These agreements between the two methods were also found in measurements of RBC aggregability in various concentrations of dextran solutions.