Multiple electrode aggregometry

Multiplate multiple electrode aggregometry (MEA) is a test of platelet function in whole blood. The test can be used to diagnose platelet disorders, monitor antiplatelet therapy, and is also investigated as a potential predictor of transfusion requirements and bleeding risk in cardiac surgery.

The Multiplate MEA Analyzer (Roche Diagnostics International Ltd) has 5 channels for simultaneous measurement of several samples or agonists. The instrument detects change in electrical impedance when platelets aggregate on metal electrodes in the test cuvette. Each cuvette contains two pairs of sensor electrodes, each of which measures the change in impedance. The duplicate sensors serve as an integrated quality control, and the analysis is accepted if the correlation coefficient of the measurements is greater than 0.98. The difference of each curve from the mean curve is also calculated, and a difference of less than 20% is accepted. The test cuvettes also contain a teflon coated magnetic stirring bar. The increase in impedance as aggregation occurs is transformed into aggregation units (AU) and plotted against time on the computer screen.

The manufacturer recommends the use of hirudin as anticoagulant for samples to be tested, but studies have shown that heparin is a good alternative. 300 µL of blood is needed for each analysis, and is diluted with the same amount of saline. After pipetting blood and saline into the cuvette, the test is incubated for three minutes before the chosen agonist is added. The test is then started, and platelet aggregation is recorded at approximately 0.5 second intervals for six minutes. Three parameters are calculated: aggregation, velocity and area under the curve (AUC). Aggregation (in AU) is the maximum height of the aggregation curve, and velocity (in AU/min) is the maximum slope of the curve. AUC is the most important parameter. It is recorded in Units (U), and is affected by both the height and the slope of the aggregation curve, and is the best overall measure of platelet activity.

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