[Evaluation of platelet aggregation test by grading curve].

In order to standardize the platelet aggregation test, we used the grading curve (GC) produced by plotting four concentrations (0.5, 1.0, 2.0 and 4.0 microM) of ADP and four concentrations (0.25, 0.5, 1.0 and 2.0 micrograms/ml) of collagen, which are aggregation inducers, along the horizontal axis and plotting their individual rates (%) of aggregation 5 minutes after administration, along the longitudinal axis. The degree of platelet aggregation was classified in 6 stages (Types III, II, I, 0, -I and -II), ranging from marked increase to marked decrease, according to the GC of ADP aggregation in healthy subjects. Type I or 0 ADP aggregation was observed in 78% of the subjects, and Type I collagen aggregation was observed in about 50% of the subjects, whereas patients with cerebral infarction showed distinct increases in Type III and II aggregations of both ADP and collagen. In most patients who were treated with antiplatelet drugs, the aggregation were Type 0, -I or -II. The concentration of inducer, which corresponded to the maximum 50% value of the GC (Max 50) was significantly correlated with the minimum concentration (threshold concentration) in ADP aggregation, at which secondary aggregation was induced even if it was reversible, and with the minimum concentration (threshold concentration) in collagen aggregation, at which the aggregation rate 5 minutes after administration increased to 50% or higher. The GC of platelet aggregation seemed to enable easy determination of the degree of aggregation, and was also considered to be useful for monitoring platelet aggregation during the administration of antiplatelet drugs.