Blood preservation is the combination of methods used to keep donated blood viable from collection to transfusion. This process supports everything from emergency trauma treatment and complex surgeries to the management of chronic conditions. By successfully storing blood, healthcare systems can maintain a ready supply for patients when needed. The ability to preserve this resource is foundational to the practice of transfusion medicine.
The Collection and Additive Process
The preservation of donated blood begins the moment it leaves the donor. Blood is collected into a specialized bag pre-filled with a chemical solution that immediately mixes with it. The primary purpose of these chemicals is to prevent coagulation and to provide nutrients to the red blood cells to keep them functional during storage.
A widely used chemical mixture is CPDA-1. Each component in this solution has a distinct function:
- Citrate: An anticoagulant that works by binding to calcium in the blood, which is necessary for the clotting cascade.
- Phosphate: Included to act as a buffer, helping to maintain a stable pH level.
- Dextrose: A sugar that the cells metabolize to produce adenosine triphosphate (ATP), their main source of energy.
- Adenine: A substance that helps red blood cells regenerate ATP, further extending their viability.
By combining these ingredients, solutions like CPDA-1 can preserve whole blood for up to 35 days.
Component Separation and Storage Methods
In modern medical practice, whole blood is infrequently transfused directly. It is separated into its primary components to allow for more targeted and efficient treatment, maximizing the utility of a single donation. The process is accomplished through centrifugation, where blood is spun at high speeds in a refrigerated centrifuge. This force causes the blood to separate into layers based on density: heavier red blood cells at the bottom, a thin middle layer of platelets and white blood cells, and lighter plasma at the top.
Red blood cells are the most frequently transfused blood component. After separation, they are stored in refrigerators at a precisely controlled temperature between 1°C and 6°C. This cold temperature slows down the metabolic processes of the cells, conserving their energy reserves. With preservative solutions like SAGM, the shelf life of red blood cells can be extended to 42 days.
Platelets have unique storage requirements that differ from red blood cells. They must be stored at room temperature, between 20°C and 24°C, and require constant, gentle agitation. This motion prevents the platelets from clumping together, which would render them ineffective. Because they are stored at a temperature that can support bacterial growth, their shelf life is short, lasting only five to seven days.
Plasma, the liquid portion of blood, is frozen soon after collection to preserve its clotting factors. When frozen within eight hours, it is known as Fresh Frozen Plasma (FFP). FFP is stored in freezers at temperatures of -18°C or colder. This deep-freezing process halts biochemical activity, giving plasma a shelf life of up to one year. From FFP, cryoprecipitate, a product rich in specific clotting factors, can also be isolated.
The “Storage Lesion” and Its Implications
Despite modern preservation techniques, stored red blood cells undergo detrimental changes over time, collectively referred to as the “storage lesion.” These biochemical and structural alterations occur during refrigerated storage and are the primary reason red blood cells have a limited shelf life. The accumulation of these changes gradually reduces the quality and effectiveness of the blood product.
During storage, red blood cells experience a depletion of key molecules. One of these is ATP, the energy currency of the cell, which is consumed faster than it can be regenerated in the cold. Another is 2,3-diphosphoglycerate (2,3-DPG), a molecule that facilitates the release of oxygen from hemoglobin to the body’s tissues. As levels of 2,3-DPG fall, the cells become less efficient at delivering oxygen.
Structurally, the cells also suffer from oxidative damage and lose the flexibility of their outer membranes. This increased rigidity makes it more difficult for the red blood cells to deform and squeeze through the body’s narrowest capillaries. These combined changes mean that older blood may be less effective after transfusion, as a percentage of the cells may be cleared from circulation more quickly.
Innovations in Blood Preservation
To overcome the limitations of standard storage, researchers are developing innovative preservation techniques. A prominent area of advancement is the cryopreservation, or freezing, of red blood cells. This method involves treating the cells with a cryoprotective agent, like glycerol, to prevent damaging ice crystals. Once treated, the red blood cells can be stored in freezers at temperatures below -65°C for up to ten years, which is useful for maintaining inventories of rare blood types.
Another focus of research is the development of improved additive solutions. Scientists are experimenting with new formulations that could better nourish red blood cells, reduce oxidative damage, and slow the progression of the storage lesion. The goal is to extend the current 42-day shelf life of refrigerated red blood cells or enhance their quality upon transfusion.
Research is also directed toward creating artificial blood substitutes. These engineered products would be designed to carry oxygen and could be universally compatible, eliminating the need for blood typing. While still in the experimental phase, a safe and effective blood substitute is a long-term objective in transfusion medicine that could address shortages.