In addition, RBC's are Rh typed and identified as "D" positive or negative.
A "screen" looks for unexpected red cell alloantibodies which may form following pregnancy or prior transfusions. If the screen is positive, the antibody is identified and 2 units lacking the corresponding antigen are crossmatched for the patient. The physician is also notified. Antibody identification can be complicated and take more than a day to complete.
A "type and cross" determines compatibility between patient serum and donor red blood cells.
Every unit crossmatched is removed from the general inventory and reserved for the patient for 72 hours. Units which are crossmatched unnecessarily will deplete Blood Bank inventories and can result in blood shortages, such as those which occurred in California after the earthquake. Blood shortages can result in cancellation of elective surgical procedures.
Blood will ordinarily not be released for transfusion until compatibility testing is completed.
However, under emergency conditions, blood products may be released without a crossmatch if the patient is in danger of dying if transfusion is delayed. In such cases, if the patient's blood type is not known, then group O Rh negative (O neg) blood can be released without compatibility testing.
In cases in which the patient's blood type is reliably known, then type-specific blood or RBC's of the same ABO and Rh group may be released.
Blood Preservation and Storage
Blood is collected as whole blood, as shown below:
Blood can be stored as whole blood (with all of the plasma present) or, much more commonly, as packed red blood cells (PRBC's) in which about 70% of the plasma has been removed. This is done by light centrifugation, as shown below:
The plasma with platelets can then be expressed off, leaving packed red blood cells (PRBC's) as shown here:
Both whole blood and PRBC's can be stored for up to 42 days at 1 - 6 degrees C.
The plasma can be centrifuged heavily a second time to separate the platelet rich plasma, as shown below:
The supernatant plasma can be expressed into a third bag and stored as fresh frozen plasma (FFP). The remaining platelet rich plasma is utilized as a platelet pack, as shown below:
As can be seen in the above diagram, a single donation of whole blood has supplied three separate components (packed red blood cells, platelets, fresh frozen plasma) that can potentially benefit three different patients.
After the expiration date, rare or valuable blood units can be "rejuvenated" with a biochemical solution that restores much of the original biochemical environment of the RBC's. The "rejuvenated" units are "washed" with isotonic saline in an automated device and then can be transfused as a saline-red blood cell suspension within 2 to 4 hours, or these units can be stored glycerolized and frozen for up to 10 years.
Cryopreservation of RBC's is done to store special, rare RBC's for up to 10 years. The RBC's are first incubated in a 40% glycerol solution which acts as an "antifreeze" within the cells. The units are then placed in special sterile containers in a deep freezer at less than -60 degrees C.
Cryopreserved units are thawed and washed free of glycerol prior to use as saline suspended RBC's. These units must be used in 2 - 4 hours to prevent possible bacterial contamination. The washed units are depleted of plasma and leukocytes.
Cryopreserved blood can help to maintain stores of Rh negative blood, to provide units for persons with antibodies to high-incidence antigens or persons difficult to cross-match because of multiple alloantibodies and to provide plasma-free blood to persons with IgA deficiency.
Thus, the types of RBC products available are:
Packed red blood cells (PRBC's)
Leukocyte depleted RBC's: cryopreserved blood that is thawed and degylcerolized is depleted of leukocytes, but much better depletion can be obtained by filtering the blood through leukocyte-specific filters.