Measurement of erythrocyte aggregation in a microchip stirring system by light transmission

In the analysis of red blood cell (RBC) aggregation using optical detection, various shearing methods have been used to disperse RBCs in confined geometries. This study investigated RBC aggregation measurement in a microchip-stirring system by analysis of light transmission. A stirring-aided disaggregation mechanism in a microchip, consisting of a flat-cylindrical test chamber (D=4 mm, H=0.3 mm) and a magnetic stirrer (d=0.14 mm, l=2.2 mm), was used to generate a given shear which was large enough to disperse RBC aggregates, but not large enough to cause any mechanical hemolysis of cells. After stirring for 10 s followed by an abrupt halt of the stirring, the intensity of the light transmitted through a microchip was measured with respect to time and analyzed. A comparative study was conducted with varying test chamber height and hematocrit. The AI and t_1/2 as typical aggregation indices obtained by analysis of transmitted light, which showed a good reproducibility (coefficient of variation (CV)<2.8%, n=10), also were found to be nearly independent of the chamber dimensions (CV<3.4%). The present aggregometry also showed the similar results of aggregation indices with varying hematocrits compared to those obtained using a laser-assisted optical rotational cell analyzer (LORCA). The essential feature of the present design is the adoption of a disposable microchip requiring a minimum blood sample volume as small as 6 μl, which enables it to be used easily in a clinical setting.