Blood has a finite shelf life. Donated blood products, such as red blood cells, plasma, and platelets, undergo changes over time that limit their usability for medical purposes. Understanding why blood expires and how to identify these changes is important for maintaining safety and effectiveness in healthcare settings.
Why Blood Has a Shelf Life
Donated blood components are delicate and have specific requirements to maintain their viability. Red blood cells are stored at cool temperatures, between 2°C and 6°C, to slow down their metabolic processes. They are also collected in bags containing anticoagulant solutions like citrate-phosphate-dextrose (CPD) or additive solutions such as saline-adenine-glucose-mannitol (SAGM) to prevent clotting and provide nutrients.
Despite these measures, red blood cells gradually degrade during storage. Their metabolic activity slows, leading to a decrease in adenosine triphosphate (ATP) and 2,3-diphosphoglycerate (2,3-DPG) levels. ATP is needed for maintaining cell membrane integrity, while 2,3-DPG helps red blood cells release oxygen to tissues. The shelf life for refrigerated red blood cells is around 42 days, a standard set by regulatory bodies like the FDA and American Association of Blood Banks (AABB).
Plasma, another blood component, can be frozen and stored for up to one year, due to its ability to preserve chemical components at very low temperatures, around -27°C or colder. Platelets, which are important for clotting, have the shortest shelf life, about 5 to 7 days, because they cannot be frozen or refrigerated without losing their function.
Identifying Expired Blood
When blood expires, visual and physical changes occur due to the breakdown of its components. Fresh, viable red blood cells appear a vibrant red. As they age and degrade, the color of the blood can darken, taking on brownish or purplish hues.
The texture of expired blood also changes significantly. You might observe clumping or sedimentation, where the blood components settle and separate into distinct layers. This separation indicates that the cells are no longer evenly suspended.
An unusual odor can also be an indicator that blood has expired. These changes result from the breakdown of red blood cells and other components, releasing byproducts that alter the blood’s appearance and smell.
What Happens to Expired Blood
When blood expires, the red blood cells undergo a process called hemolysis, where their membranes rupture. This releases hemoglobin into the storage solution, which can then be seen as “cell-free hemoglobin.” The degradation also leads to the breakdown of proteins and the accumulation of waste products within the blood bag.
These biological changes diminish the blood’s therapeutic function. For example, the red blood cells lose their ability to effectively carry oxygen due to reduced levels of 2,3-DPG. Transfusing expired blood is avoided because it offers little therapeutic benefit and can cause adverse reactions in the recipient.
Such reactions can include hemolytic transfusion reactions, where the recipient’s immune system attacks the damaged red blood cells, leading to symptoms like fever, chills, back pain, and dark urine. Any units that reach their expiration date are discarded as biohazardous waste.