We read with interest the article by Ben-Tal and coworkers 1 who reported that concentrations of prothrombin, Factor (F) VII, F IX, FX, and fibrinogen remained stable in plasma that had been twice-frozen and stored at -80 ∞ C. These data support their conclusion that this component can be used safely for transfusion as a source of vitamin K-dependent clotting factors and fibrinogen, but do not provide information on the use of this component for replacing protein C, protein S, or antithrombin III. We performed the following study to provide data on the stability of these proteins in twice-frozen fresh frozen plasma (FFP).Ten units of FFP were prepared from whole blood collected in citrate phosphate dextrose (Macopharma, Mouvaux, France). The units were thawed and 5-mL aliquots were removed by sterile technique (first thaw, Time 0). Concentrations of protein C, protein S, and antithrombin III were measured using a coagulation analyzer (IL Futura, Instrumentation Laboratory, Warrington, UK). The thawed units were stored at 4 ∞ C for 24 hours, and another sample was obtained (first thaw, Time 24). The units were refrozen at -80 ∞ C for 1 week, and a third sample was obtained immediately after thawing (second thaw, Time 0) and a fourth sample 24 hours later (second thaw, Time 24).The results of factor measurements (Table 1) show that although there are individual variations in the plasma concentrations of protein C, protein S, and fibrinogen among normal blood donors, these proteins remain stable after two thaws and storage at 4 ∞ C for two 24-hour periods. We believe that these findings complement those of Ben-Tal and colleagues, indicating that twice-frozen and thawed plasma is suitable not only for replacing vitamin K-dependent coagulation factors, but also for replacing protein C, protein S, and antithrombin. Also, using twicefrozen and thawed plasma may significantly reduce wastage of thawed and unused FFP. Muttuswamy Sivakumaran, MSc, FRCP, FRCPath, PhD
