Freezing of plasma and recovery of factor VIII.

The freezing procedure and its influence on the plasma quality was studied with a new plasma container and freezing bath and compared with the results from those obtained with commonly used equipment. Cryoprecipitation was performed on plasma pools frozen at three different rates, and quality and recovery of the cryoprecipitates were determined by analysis of factor VIII, factor VIII-related antigen (vWF:Ag), and fibrinogen. The plasma freezing time was 95 and 65 percent shorter with a new -40 degrees C freezing bath as compared to -25 and -80 degrees C freezing boxes, respectively. A further 30 percent reduction of the plasma freezing time was gained by the introduction of a new flat 750-ml plasma container. Rapid plasma freezing prevented substantial loss of factor VIII in frozen plasma. Cryoprecipitate purity measured as factor VIII-to-fibrinogen ratio increased from 0.50 to 0.82 (IU/mg) when the freezing time was decreased from 10 hours to 45 minutes, although the recovery of factor VIII increased less. In summary, freezing of plasma in small flat containers in an effective ethanol bath resulted in rapid freezing with high recovery of factor VIII in plasma, and increased purity and recovery of subsequently processed cryoprecipitate. This freezing concept, adapted at Swedish blood banks, has contributed to higher source plasma quality and increased self-sufficiency.