AbstractLyophilized reagents are used on a daily basis in coagulation diagnostics. They often contain a number of excipients in addition to the active compound. Some of these excipients may, however, influence coagulation dynamics.Besides from plasmatic coagulation bulking agents may influence platelet properties. We therefore studied the influence of a variety of bulking agents (glycine, mannitol, sucrose and trehalose) as well as a surfactant (TweenBoth disaccharides as well as TweenWhile the influence observed for glycine may be due to fibrinogen precipitation, the mechanism of mannitol appears to be more complex as platelet function as well as fibrin-based clot formation are influenced. This study therefore demonstrates the necessity to check for coagulation impairment due to compounds contained in lyophilized reagents.