Objective: This study aimed to investigate the in vitro effects of hydroxyethyl starch (HES) solutions of different molecular weights and 0.9% isotonic NaCl on platelet aggregation functions using aggregometry.

Material and Method: Whole blood samples were collected from 20 healthy individuals. Platelet aggregation was assessed via aggregometry following dilution with HES 130, HES 200, HES 450, and 0.9% isotonic NaCl solutions.

Results: The aggregation slope values were not affected by any of the dilution solutions. However, the high-molecular-weight HES solution (HES 450) induced hyperaggregation, as evidenced by an increase in the maximal aggregation value. In ADP-induced aggregation (10 μM), no significant difference was observed in maximal aggregation values between the dilution groups and the control (p =0.225). In ristocetin-induced aggregation, the HES 450 group exhibited a statistically significantly higher maximal aggregation value compared to other groups (p =0.0063). Similarly, in collagen-induced aggregation, the maximal aggregation values for the HES 450 group were significantly different from those of the control group (p =0.0137).

Conclusion: The in vitro hyperaggregation effect of high-molecular-weight HES demonstrated in this study has not been widely reported previously. Based on our findings and previous literature, we propose that this effect may be mediated by HES binding to von Willebrand factor (vWF) and fibrinogen after coating the platelet surface, thereby enhancing platelet aggregation.