Freezing technique and quality of fresh-frozen plasma.
Cell-poor plasma was prepared by apheresis from 10 donors. From each donor, an amount of 200 ml was frozen rapidly to -40 degrees C in standard blood bags, and a further 200 ml was frozen slowly to -20 degrees C. Before freezing and after thawing, plasma samples were collected and frozen to -70 degrees C pending analysis. Coagulation factor VIII activity was reduced to 90% by rapid freezing and to 80% by slow freezing. Factor V was not influenced by rapid freezing, but slow freezing reduced the levels to 92% of the pre-freezing levels. In some of the plasma bags a slight increase in fibrinopeptide A occurred. However, soluble fibrin, thrombin-antithrombin complexes and spontaneous proteolytic activity were not altered by freezing. The beta-thromboglobulin increased slightly with slow freezing. Moreover, in a separate experiment, evaluating the possible effects of refreezing plasma samples, an increase in beta-thromboglobulin was also recorded, while the levels of factors VIII and V and von Willebrand factor were not affected. The changes in some variables, which were recorded in the cell-poor plasma, frozen soon after the blood donation at a slow freezing rate, must be regarded as insignificant in most clinical situations.