Abstract
Low-grade contact activation of hemostasis is clinically relevant. Freezing/thawing of plasma was studied in the intrinsic coagulation activity assay. Normal plasmas were frozen at −80°C or −20°C and thawed at 37°C or 23°C. These plasmas and unfrozen samples were activated by SiO2 -CaCl2. Freezing/thawing of normal plasma induced about 100-fold more thrombin activity at 5 minutes coagulation reaction time than the respective unfrozen samples. Freezing at −80°C induces more artificial changes than freezing at −20°C. In 9 of 10 plasmas of patients receiving coumarin, nearly no additional thrombin is generated within a 12-minute coagulation reaction time. Minor procoagulant changes of plasma might be dangerous in patients with insufficient liver function, who might not tolerate a therapy with fresh frozen plasma, which behaves as a procoagulant because of its matrix changes. The intrinsic coagulation activity assay allows the measurement of low-grade contact activation of frozen/thawed plasma.