Background: Light transmission aggregometry is a standard method used to evaluate platelet function. However, in clinical settings, light transmission aggregometry results sometimes fail to reflect actual platelet hyperactivity. In patients with suspected platelet hyperactivity such as thrombosis, platelet aggregates are frequently detected in citrated blood samples using a scattergram of a hematology analyzer. This study aimed to evaluate the effects of platelet aggregate formation on light transmission aggregometry results.

Methods: We used 19 citrated blood samples in which platelet aggregate formation was intentionally induced by a hematology analysis process. Employing fully automated light transmission aggregometry and agonists including adenosine diphosphate or collagen, light transmission aggregometry maximum aggregation percentage, platelet count, and mean platelet volume of platelet-rich plasma before and after platelet aggregate formation were evaluated.

Results: Light transmission aggregometry maximum aggregation percentage with adenosine diphosphate or collagen was significantly lower in the samples after than before platelet aggregate formation. Platelet count and mean platelet volume were both decreased by platelet aggregate formation (P < .01), suggesting that maximum aggregation percentage reduction was caused by the decrease in activated large platelets in the platelet-rich plasma.

Conclusion: This study clarified that platelet aggregate formation in blood samples interfered with an accurate assessment of platelet hyperactivity. To ensure reliability of light transmission aggregometry results, we must confirm that platelet aggregates have not formed in the sample, especially in those of patients with platelet hyperactivity.