A blood pack is a sterile, flexible plastic bag used to collect, store, and transfuse blood. It typically holds around 450 to 475 milliliters of blood (roughly one pint) and contains a premixed anticoagulant solution that prevents the blood from clotting. Blood packs are the standard container used by blood banks, hospitals, and transfusion services worldwide, and their design has a direct impact on how long donated blood stays viable.
What a Blood Pack Is Made Of
The bag itself is made from polyvinyl chloride (PVC), a flexible plastic. On its own, PVC would be too rigid, so manufacturers add a softening agent called a plasticizer. The most common plasticizer is DEHP (di-2-ethylhexyl phthalate), which does more than just make the plastic pliable. DEHP slowly leaches from the bag wall into the stored blood, where it stabilizes red blood cell membranes. This reduces swelling, limits damage, and improves the percentage of cells that survive after transfusion.
Because DEHP is a phthalate, and phthalates raise health concerns at high exposure levels, researchers have tested alternatives. One called DINCH comes close to matching DEHP’s protective effect on red blood cells while leaching less readily from the plastic. Another alternative, BTHC, performs noticeably worse, with stored cells losing more hemoglobin and breaking down faster. For now, DEHP remains the most widely used plasticizer in blood storage bags.
Before plastic bags existed, blood was collected in glass bottles. Glass posed real problems: its rough inner surface promoted clotting, the rigid container caused more red blood cell destruction during collection, and the bottles couldn’t be squeezed or easily connected to tubing. Plastic bags allow gentler blood flow, reduce cell damage, minimize foam formation, and have smooth surfaces that lower clotting risks. The switch from glass to plastic happened over 50 years ago and remains one of the most significant advances in transfusion medicine.
The Solution Inside the Bag
When you look at an empty blood pack before collection, it already contains a clear liquid. This is an anticoagulant-preservative solution, most commonly CPDA-1. A standard 450 mL collection bag holds 63 mL of this solution, which contains five key ingredients: sodium citrate binds calcium in the blood to prevent clotting, citric acid maintains the right pH, dextrose (a simple sugar) feeds the red blood cells during storage, phosphate supports cell energy metabolism, and adenine helps cells regenerate their main energy molecule, ATP.
Without adenine, red blood cells can only be stored for about three weeks. Adding it in the 1970s pushed storage time to five weeks, a meaningful jump that gave blood banks more flexibility in managing their supply.
How One Donation Becomes Multiple Products
Most blood packs aren’t single bags. They come as systems of two, three, or four bags connected by tubing, often called satellite bag systems. After whole blood is collected into the primary bag, it goes into a centrifuge that separates the blood by weight. The heavier red blood cells settle to the bottom while the lighter plasma rises to the top. Platelets sit in a middle layer.
A technician then transfers the plasma into one satellite bag and, if needed, platelet-rich plasma into another. The connecting tubing is sealed and cut, creating separate, individually labeled products from a single donation. This means one blood pack system can treat up to three different patients: one needing red cells, another needing plasma, and a third needing platelets.
Additive Solutions That Extend Shelf Life
After the plasma is removed, the concentrated red blood cells in the primary bag are often mixed with a second preservative called an additive solution. In Europe, the standard is SAGM, which contains saline, adenine, glucose, and mannitol. In the United States, AS-1 and AS-3 are more common, using citrate instead of mannitol to protect cell membranes.
Mannitol and citrate serve the same basic purpose: they stabilize the red blood cell membrane and prevent it from breaking open during weeks of cold storage. The addition of these solutions pushed the usable shelf life of red blood cells to 42 days (six weeks), up from the five-week limit with CPDA-1 alone. After six weeks of storage, both SAGM and AS-3 maintain 78 to 84 percent cell recovery with only about 0.4 percent of cells destroyed, well within safety standards.
Storage Conditions
Red blood cells must be refrigerated at 2 to 6°C from the moment processing is complete. Standard red cell units last 42 days at this temperature. Pediatric red cell units, which are smaller portions drawn from the same donation, have a 35-day shelf life. Washed red cells, which have had the plasma proteins rinsed away for patients with severe allergic reactions, must be used within 28 days.
Plasma, by contrast, is frozen and can be stored for up to a year. Platelets are kept at room temperature on a gentle rocker that prevents them from clumping, but they expire in just five days, making them the most perishable blood product.
Built-In Filters
Many modern blood pack systems include an integrated filter that removes white blood cells before storage, a process called leukoreduction. White blood cells from the donor serve no purpose for the recipient and actually cause problems. They trigger febrile (fever) transfusion reactions, which are the most common adverse reaction to blood transfusion. They also stimulate the recipient’s immune system to form antibodies against donor tissue, a particular concern for patients who need repeated transfusions over months or years.
Current-generation filters reduce white blood cell counts by more than 99.99 percent, bringing the total below 5 million cells per unit. Before leukoreduction became routine, about 4 percent of transfusions caused febrile reactions. After its introduction, that rate dropped to around 1 percent. The filters use layers of synthetic fibers that trap white cells while allowing red blood cells and platelets to pass through.
Labeling and Traceability
Every blood pack carries a label that follows an international coding system called ISBT 128. The FDA recognizes this standard for all blood and blood component container labels in the United States, with the current version (4.0.0) updated in January 2024. The label includes a unique donation identification number, the blood type, the product type, the expiration date, and barcodes that allow the unit to be tracked from the donor’s arm through processing, storage, and ultimately to the patient who receives it. This traceability is critical for investigating any transfusion reaction and for recalling products if a donor later reports an illness.