Blood donation involves collecting a unit of whole blood and separating it into components for patient transfusion. This component-based approach ensures patients receive only the specific part of the blood they require. Components like red blood cells, platelets, and plasma each serve a unique function, requiring different storage environments and possessing a finite shelf life. The viability of a blood bag is strictly determined by its biological contents and the preservation methods used to maintain function outside the human body.
The Standard Shelf Life of Red Blood Cells
Red blood cells (RBCs) are the most frequently transfused component, and their shelf life is determined by the need to maintain their oxygen-carrying capacity. Most red cell units are stored in specialized blood bank refrigerators at a precisely controlled temperature range of 1 to 6 degrees Celsius, which significantly slows down the cells’ metabolic rate. This cold environment, however, is not enough on its own to prevent degradation over time.
To achieve an extended shelf life, the collected RBCs are suspended in a preservative solution that serves two primary purposes: anticoagulation and nutrient supply. The initial solutions, such as Citrate-Phosphate-Dextrose-Adenine (CPDA-1), were designed to prevent clotting and provide adenine to help the cells synthesize adenosine triphosphate (ATP), extending the storage limit to 35 days.
Modern transfusion medicine now commonly uses additive solutions, such as AS-1, AS-3, or AS-5, which are added after the plasma has been removed from the whole blood unit. These solutions contain a mixture of saline, dextrose (as a sugar source), and adenine, which further supports the red cells’ energy needs and helps maintain their integrity. The use of these advanced additive solutions allows red blood cell units to be stored for a maximum period of 42 days.
The 42-day limit ensures that at least 75% of the transfused red cells survive in the recipient’s circulation 24 hours after transfusion. Although the cold temperature slows the metabolic process, the effectiveness of the preservative solutions gradually diminishes over time, meaning degradation continues.
How Long Other Blood Components Last
The biological nature of other blood products necessitates different storage conditions and results in varied shelf lives. Platelets, small cell fragments responsible for clotting, have the shortest lifespan of all major components. To maintain function, platelets must be stored at room temperature, specifically between 20 and 24 degrees Celsius, requiring constant, gentle agitation.
This warm storage prevents premature aggregation but creates a high risk of bacterial growth, which is the primary factor limiting shelf life. Consequently, platelet units are viable for a maximum of 5 to 7 days from collection. This short window creates a continuous demand for donations to maintain an adequate supply.
In contrast, plasma, the liquid portion of the blood containing proteins and clotting factors, can be preserved for a much longer duration. Plasma is separated from the red cells and rapidly frozen at very low temperatures, typically below -25 or -30 degrees Celsius, to preserve the delicate clotting proteins. Once converted to Fresh Frozen Plasma (FFP), the unit can be stored for up to one year.
Freezing halts biological activity within the plasma, allowing for long-term inventory management, a significant advantage over red cells and platelets. When needed, the frozen unit must be thawed in a controlled environment. Once thawed, its shelf life is drastically reduced, usually lasting only 24 hours to five days depending on the specific product.
The Science of Blood Preservation and Expiration
The expiration of a blood bag is a result of progressive cellular and biochemical changes that occur even under refrigerated conditions, collectively known as the storage lesion. Red blood cells, which lack a nucleus and mitochondria, rely on a process called anaerobic glycolysis to produce their energy molecule, ATP. During storage, the red cells continuously consume the glucose in the preservative solution, leading to a gradual depletion of their energy reserves.
As glucose is metabolized, the cells produce lactic acid, which accumulates and causes the pH to drop. This acidic environment, combined with low ATP levels, leads to a loss of cell membrane flexibility. The cells become stiff and lose their biconcave shape, making them less capable of navigating narrow capillaries and leading to premature destruction upon transfusion.
Another change is the loss of 2,3-diphosphoglycerate (2,3-DPG), a compound that helps hemoglobin release oxygen to tissues. When 2,3-DPG levels fall, red cells hold onto oxygen more tightly, temporarily impairing delivery immediately following transfusion. The accumulation of potassium, which leaks out as membrane integrity degrades, must also be monitored, especially for large-volume transfusions.
The strict time limits are enforced because these biochemical changes are irreversible and progressive, eventually compromising the red cells’ ability to survive and function in the recipient. For platelets, the higher storage temperature accelerates their metabolism and significantly increases the risk of bacterial proliferation, which mandates their short 5- to 7-day expiration window.