Red blood cell aggregation measurements in whole blood and in fibrinogen solutions by different methods

Red blood cell (RBC) aggregation is an important component of whole blood v iscosity, especially at low shear rates, and is the major cause of the non- Newtonian flow properties of normal blood. In different laboratories severa l methods are used to determine RBC aggregation, therefore the standardizat ion of aggregation measurements is especially important for getting compara ble results. Aggregation indices of 62 human blood samples were determined by two different methods; LORCA (Laser-assisted Optical Rotational Cell Ana lyzer) and Myrenne aggregometers and related to plasma fibrinogen concentra tion. Our results show closer correlation values between RBC aggregation an d fibrinogen concentration, when RBC aggregation was measured by LORCA (p < 0.001), although correlation could be revealed with Myrenne, when plasma f ibrinogen level was less than 4.5 g/l. Correlation coefficient between aggr egation indices measured by LORCA and Myrenne aggregometers was also closer below this fibrinogen level. In vitro examination of RBC aggregation in fi brinogen solutions showed that higher fibrinogen concentration results in h igher RBC aggregation only up to a certain level similarly to that found in human whole blood samples. Our results show that plasma fibrinogen level h as an important, concentration dependent effect on RBC aggregation in human blood, but above a certain level it may not cause further aggregate format ion.