Quantitation of platelet mass during aggregation in the electronic (Wellcome) whole blood aggregometer

A new electronic aggregometer has been described which measures platelet aggregation by monitoring the changes in electrical impedance that occur when a platelet aggregate forms between two electrodes (Cardinal and Flower, 1980). To validate the instrument, the protein content of the platelet aggregate was estimated by the Lowry method (Lowry et al., 1951). Aggregating agents used were ADP (doses (mu mol), 1.0, 0.1, 0.01, 0.005, 0.0025 and 0.001), Thrombin (doses (units) 0.25, 0.20, 0.15, 0.10 and 0.05) and Collagen (doses (micrograms) 20.0, 15.0, 10.0, 5.0, 1.0 and 0.5). The quantity of protein was correlated with the dose of aggregating agent and with 6 characteristics of the aggregation curve. Linear correlation coefficients of the former were 0.92 (Log dose ADP), 0.91 (Thrombin dose) and 0.86 (Collagen dose). Correlation coefficients (Electrode Protein against curve characteristics), were greater than 0.87 for all aggregating agents and the extent of aggregation (ohms), percent of maximum aggregation, percent of maximum aggregation at 6 minutes, and maximum rate of aggregation (ohms/s). Linear correlation coefficients for the curve characteristics, time to maximum aggregation(s) and time to 50% of maximum aggregation(s), for ADP and Collagen were greater than 0.70. However, correlation coefficients of the above two characteristics to Thrombin were 0.32. We have concluded that the maximum extent of aggregation is the best method of assessing platelet aggregation with the electronic aggregometer.