Editor’s note: This article extends the discussion of plasma-based transfusion therapy and the role of albumin from this and last month’s issue of rvetILLINOIS.
Ideally, if plasma is to be frozen for the purpose of longer-term storage, it should be prepared from whole blood within 8 hours of collection and frozen within 1 hour of separation to be stored as fresh frozen plasma (FFP). However, one study confirmed highly therapeutic coagulation factor and hemostatic protein content in plasma frozen even after 24 hours of ambient whole blood storage.
In human transfusion medicine this product is termed FP24. When stored at -18°C, these products are considered stable for 1 year, after which time the product is relabeled as frozen plasma.
Frozen plasma retains albumin and globulins but is not considered a therapeutic source of labile factors V and VII. The factor activity and hemostatic potential of canine FFP immediately after thawing is very similar to that of the thawed then refrigerated product (called thawed plasma, or TP). As such, many human and veterinary hospitals now retain units of thawed plasma on hand for emergency use. This offers an advantage over FFP because it eliminates the time required to optimally thaw the product, which can exceed 30 minutes.
Several veterinary studies have compared FFP to canine thawed plasma at various storage lengths and, although some loss of factor activity is noted, these differences are thought to be clinically irrelevant. Canine thawed plasma is also quite similar to liquid (never frozen) plasma, even at 35 days of refrigerated storage, and bacterial cultures were negative in one study for this duration.
Plasma can be further fractionated into cryoprecipitate and cryosupernatant (or cryopoor plasma). Following a slow, cold thaw and centrifugation of FFP, thecold-insoluble proteins are sedimented and retained below the supernatant. This sediment product contains fibrinogen, vWF, factor VIII complex, factor XIII, and fibronectin, all in a very small volume.
Cryosupernatant (or cryopoor plasma) is expressed off of cryoprecipitate and serves as a source of all factors other than those concentrated in cryoprecipitate, as well as albumin, globulin, and the natural anticoagulants antithrombin and protein C and S. After sedimentation, cryoprecipitate is immediately refrozen or lyophilized for storage. Cryopoor plasma can also be frozen for storage but is difficult to obtain commercially in the U.S.; it is available in the UK.
Further processing of plasma allows for the manufacture of plasma derivatives, such as immunoglobulin, factor concentrates, and purified albumin. Canine-specific albumin is currently available for the veterinary market. This is prepared using a modified heat shock method (heating, then concentration by precipitation, and ultrafiltration).
Albumin is sold as a lyophilized product and is conveniently stored at room or refrigerated temperature for several years.
By Erin Long, DVM, DACVECC
