The ability to store and preserve donated human blood is a significant achievement in modern medicine. Blood preservation techniques maintain the full therapeutic function of blood components for extended periods. This process is the foundation of blood banking, ensuring a readily available supply for trauma care, complex surgical procedures, and the treatment of chronic conditions like anemia. Sophisticated methods stabilize this delicate biological material, allowing medical facilities to manage inventories and respond to patient needs worldwide.
Separating Blood for Storage
A unit of whole blood is not typically transfused directly but is processed into its individual components immediately following donation. This separation maximizes the utility of a single donation, as different medical conditions require specific components for treatment. The primary components collected and preserved are Red Blood Cells (RBCs), Plasma, and Platelets.
The physical process used for component breakdown is centrifugation, which spins the blood at high speeds within a refrigerated machine. Because blood components have different densities, the centrifugal force causes them to settle into distinct layers. Red blood cells form the densest bottom layer, while the less dense plasma rises to the top, and a middle layer, known as the “buffy coat,” contains the platelets and white blood cells.
Once separated, each component is channeled into its own dedicated satellite bag using a sterile, closed system to maintain integrity and prevent contamination. This component-based approach allows blood centers to optimize preservation methods, as storage requirements vary widely for each fraction. Preparing these products is time-sensitive, particularly for platelets and plasma, which must be processed within a few hours of collection to retain full potency.
Standard Storage Methods and Shelf Life
The vast majority of blood products are preserved using routine, short-to-medium-term storage methods relying on precise temperature control and specialized chemical solutions. Red Blood Cells (RBCs) are stored under refrigeration at $2^\circ\text{C}$ to $6^\circ\text{C}$. This chilled environment slows the cells’ metabolic rate, extending their viability far beyond their normal lifespan.
To support the cells during storage, the blood is mixed with an anticoagulant and a nutrient solution. Early solutions like CPD (Citrate-Phosphate-Dextrose) were improved by adding Adenine, creating CPDA-1. This solution provides glucose for cellular energy production and adenine to maintain the red blood cell’s energy molecule, ATP. CPDA-1 allows RBCs to be stored for up to 35 days.
Further preservative solutions, such as AS-1 (Adenine-Saline-Glucose-Mannitol), have extended the maximum shelf life for refrigerated RBCs to 42 days. These solutions stabilize the cell membrane and provide a continuous energy supply. This ensures that at least 75% of the red cells remain viable and functional after transfusion. Maintaining this strict cold chain from collection to the patient is necessary, as any temperature fluctuation can quickly compromise the unit’s quality and safety.
Plasma, the liquid component rich in clotting factors and proteins, requires a different approach to preserve its delicate functional molecules. It is typically frozen rapidly, often using a blast freezer, and stored at $-30^\circ\text{C}$ or colder. This deep freeze halts enzymatic activity and degradation, allowing Fresh Frozen Plasma to maintain its full complement of clotting factors for up to one year.
Platelets, which are small cell fragments responsible for initiating blood clotting, have the shortest storage duration. They must be maintained at a controlled room temperature of $20^\circ\text{C}$ to $24^\circ\text{C}$. Since this temperature promotes bacterial growth, they require continuous, gentle agitation to prevent aggregation and ensure oxygen exchange. This storage method allows platelets to be used for only five to seven days before they must be discarded.
Cryopreservation for Extended Viability
When storage longer than the standard 42-day limit is necessary, Red Blood Cells undergo cryopreservation (deep freezing). This technique is reserved for maintaining inventories of rare blood types, supporting military reserves, or storing units for autologous donation. Cryopreservation extends the shelf life of RBCs, enabling storage for 10 years or longer when maintained at ultra-low temperatures, such as $-80^\circ\text{C}$.
The primary challenge in deep freezing is preventing ice crystal formation, which can rupture red blood cell membranes and lead to hemolysis. To counteract this damage, a cryoprotectant compound is introduced before freezing. Glycerol is the most commonly used cryoprotectant for red cells, typically added at a high concentration (40% weight/volume).
Glycerol permeates the cell membrane and reduces the concentration of solutes inside the cell, lowering the freezing point and minimizing intracellular ice formation. Following extended storage, the blood unit must undergo thawing and washing, known as deglycerolization, before transfusion. This washing is necessary because the high concentration of glycerol is toxic to the recipient and must be removed to prevent osmotic injury.
Deglycerolization involves a series of washes with progressively decreasing saline concentrations in an automated centrifuge. This step-wise dilution slowly removes the glycerol, preventing the rapid osmotic swelling and rupture that would occur otherwise. Although this post-thaw washing process is time-consuming, it is necessary to ensure the safety and viability of the long-term preserved red cells.
Ensuring Safety Before Transfusion
Maintaining blood safety requires rigorous quality control measures from donation through to transfusion. Before any unit is released for clinical use, it undergoes comprehensive screening for transfusion-transmissible infectious diseases. This testing includes highly sensitive assays for pathogens such as Human Immunodeficiency Virus (HIV), Hepatitis B and C viruses, and West Nile Virus.
If any screening tests are reactive, the entire donation is permanently removed from the blood supply, and the donor is notified. These laboratory procedures detect evidence of infection, often using molecular methods like Nucleic Acid Testing (NAT) to identify viral genetic material. NAT can detect a recent infection even before the body has produced antibodies.
Beyond infectious disease screening, safety requires accurate blood typing and cross-matching to guarantee compatibility. All donated blood is typed for the ABO and Rh systems, which identify specific antigens on the red blood cells. Compatibility testing (cross-matching) confirms that the recipient’s plasma does not contain antibodies that would react destructively with the donor’s red cells. These stringent protocols minimize the risk of adverse reactions and maintain a secure blood supply.