Adenosine diphosphate-induced platelet aggregation correlates with platelet activation identified with the use of flow cytometry.

Background: Assessment of the likelihood of platelet activation (i.e. platelet reactivity) identifies patients at high and low risk of subsequent thrombotic events. Turbidometric platelet aggregation has been used to assess platelet function for more than 4 decades. We have developed a method to assess individual components of platelet activation with the use of flow cytometry that is performed in minimally altered whole blood.

Aims: To compare assessment of platelet reactivity determined with the use of aggregometry and flow cytometry.

Material And Methods: Twenty adult patients with atherosclerotic vascular disease were included in this study. Blood from each patient was used to determine turbidometric platelet aggregation and to assess platelet activation by flow cytometry. ADP was used as the agonist. Values are means +/- SEM. Comparison was performed with the use of Student's t test and correlation was assessed with the use of Pearson's correlation analysis.

Results: Both maximal aggregation and the slope of aggregation correlate with the percentage of platelets that bound fibrinogen in response to 0.2 microM ADP. The best correlation was seen between the slope of aggregation induced by 0.2 or 1 microM ADP and the percentage of platelets that bound fibrinogen in response to 0.2 microM ADP (for 0.2 microM r = 0.62, p = 0.038; for 1 microM r = 0.71, p = 0.025).

Conclusion: The binding of fibrinogen to activated platelets assessed with the use of flow cytometry correlates best with the slope of turbidometric aggregation and appears to reflect the propensity of platelets to activate.