A comparison of five methods for estimating red cell aggregation.

A comparison has been made of the responses of five techniques for estimating the degree of aggregation in red cell suspensions. They were the use of direct microscopic observation, the erythrocyte sedimentation rate test, low shear rate viscometry, the Myrenne Erythrocyte Aggregometer and the Paar Oscillating Capillary Rheometer. The test samples consisted of normal red cells suspended in buffer to which fibrinogen was added as an aggregating agent. Each test exhibited a fibrinogen threshold concentration before any response occurred. The range of response and sensitivity was highest for the sedimentation test, viscometry and the Paar device. However the simplicity and rapidity of operation of the Myrenne machine make it attractive in a clinical setting. Finally, inspite of its relative insensitivity, the microscopic technique has the great advantage of being the only one that produces unequivocal data since it is based on direct observation.