EVALUATION OF ELECTRICAL AGGREGOMETRY - COMPARISON WITH OPTICAL AGGREGOMETRY, SECRETION OF ATP, AND ACCUMULATION OF RADIOLABELED PLATELETS

Abstract

Platelet aggregation [in humans] has been most commonly studied in vitro by measuring increases in light transmission as platelets aggregate in PRP [platelet-rich plasma]. Recently, an electrical impedance method for measuring platelet aggregation was introduced. This method can be used with either PRP or whole blood and measures an increase in impedance across electrodes placed in the blood samples as platelets accumulate on them. The results obtained by the 2 methods are compared, using ADP and collagen as aggregating agents, and the secretion of platelet ATP was measured simultaneously. Although the aggregometry results were similar, recordings obtained by the electrical method did not distinguish 2 waves of platelet aggregation or correlate with secretion as well as recordings obtained by the optical method. When PGI2 [prostaglandin I2] or PGE1 was added to the PRP, both the rate and extent of the increase in light transmittance were inhibited, but the main effect on the increase in impedance was a decrease in its rate and not in its extent. Increases in impedance and secretion of ATP were also measured in whole blood after the platelets were labeled with a 125I-containing antibody specific for platelet surface glycoproteins. The increases in impedance lagged several minutes behind the formation of platelet aggregates and the secretion of platelet ATP. Apparently, there are advantages and disadvantages to both methods of measurement of platelet aggregation and the parameters being measured must be clearly understood to properly interpret the results.