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Frozen Blood Products
Cryopreservation of blood products, which maintains their activity, is an effective way to increase their storage time. Plasma products are routinely stored frozen, but RBCs are sometimes cryopreserved (for cryopreserved hematopoietic progenitor cell products, see Chapter 84, Chapter 85 ). Rarely, platelet products are cryopreserved, but the recovery is low and the product is still under investigation and not FDA licensed. The primary indication for freezing RBCs is the preservation of rare and/or autologous units. Additional indications include inventory management during emergencies or shortages and military contingency operations. RBC products are usually cryopreserved with glycerol. Before use, the product must be thawed and deglycerolized. Frozen RBCs are not routine transfusion practice because of the increased cost (both labor and equipment) and RBC loss during the process.
Cryopreserved RBC Products
Cryopreserving RBCs is a valuable technology to prolong storage of rare units (e.g., RBCs lacking high-frequency antigens). Freezing RBCs increases their storage time to 10 years (and likely even longer) and also provides a product with replenished 2,3-diphosphoglycerate (2,3-DPG) and adenosine triphosphate (ATP) levels. Frozen and deglycerolized units have a decreased number of leukocytes (∼9 × 10 6 white blood cell unit) but too many for labeling as leukoreduced. After thawing and deglycerolization up to 20% of the RBCs can be lost. Because of the removal of the supernatant plasma and storage solution, restored ATP and 2,3-DPG, thawed and deglycerolized RBC products may be preferred in some situations, such as neonatal RBC exchange and intrauterine transfusion.
Cryopreservation With Glycerol
RBCs must be protected during freezing to prevent cellular dehydration and mechanical trauma as a result of intracellular ice formation. Glycerol is a penetrating cryoprotective agent, which crosses the cell membrane into the cytoplasm, providing an osmotic force that prevents water from migrating outward as extracellular ice is formed. Glycerol must be introduced slowly, as rapid introduction can itself result in hypertonic damage and hemolysis. RBC units are frozen using either a high- or low-glycerol method. Low, 15%–20%, concentrations of glycerol require the use of liquid nitrogen to achieve rapid cooling rates (−100°C/minutes) and are limited to polyolefin bags. These products are then stored at ≤−120°C. High, 40%–50% concentrations of glycerol are required for slower cooling rates (−1°C/minutes) achieved with mechanical freezers (≤−80°C). They can be frozen in either polyvinyl chloride (PVC) bags or polyolefin (preferred because they are less brittle) and stored at ≤−65°C. Most blood centers use the high-glycerol method.
RBCs collected and stored in citrate phosphate dextrose (CPD) or citrate phosphate dextrose adenine (CPDA-1) for up to 6 days, or up to 3 days postexpiration if rejuvenated, can be frozen. RBC units stored in CPD/additive solution-1 (AS-1) or CP2D/AS-3 can be stored up to 42 days before freezing. RBCs stored in CPD/AS-1 can be rejuvenated then frozen but can only be stored frozen for up to 3 years. Frozen RBCs are FDA approved for storage up to 10 years; however, there are reports of successful use of RBCs frozen up to 37 years. An aliquot of the donor’s serum or plasma should be frozen and stored for possible use if new donor screening tests are implemented.
Rejuvenation
FDA-approved rejuvenation solutions contain pyruvate, inosine, phosphate, and adenine. They are not intended for intravenous administration; after incubation with the solution, the RBC units are either frozen or washed and stored at 1–6°C for up to 24 hours. The solution may be added at any time between 3 days after collection and 3 days after expiration of the unit. Use of rejuvenation solution for liquid units less than 14 days of age is not recommended because the cells can develop supraphysiologic levels of 2,3-DPG resulting in decreased oxygen affinity.
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