Platelet aggregation: The use of optical density fluctuations to study microaggregate formation in platelet suspension

A new approach to the investigation of microaggregate formation kinetics in platelet suspension is described. The method is based on the analysis of light transmission fluctuations produced by the changes in the number of platelets in optical channel. The relative dispersion of such fluctuations (D) was used as a parameter to estimate the degree of platelet aggregation and to analyze the aggregation kinetics. It was found that a continuous recording of this parameter allows to detect microaggregate formation during spontaneous aggregation and aggregation induced by very low concentrations of ADP (0.05–0.15 uM) in platelet-rich citrate plasma. When 3–10 uM ADP was added to acid citrate-dextrose anticoagulated plasma at pH 6.5, microaggregate formation was detected by increase in D, whereas light transmission decreased by 15–20%. Analysis by scanning electron microscopy and the use of standard inhibitors of aggregation confirmed that in all these cases the microaggregate formation did take place.