A blood pack is a specialized, sterile, and closed system container used to collect whole blood from a donor for processing and transfusion. It contains an anticoagulant solution that prevents the blood from clotting immediately after collection. Blood packs are fundamental to modern healthcare, providing products necessary for complex surgeries, trauma care, and managing chronic medical conditions.
The Components of Whole Blood
Whole blood is a mixture of liquid and cellular components, including plasma, red blood cells, white blood cells, and platelets. These components are organized by density and can be separated using laboratory techniques.
Red blood cells (erythrocytes) are the most numerous cellular element, making up about 45% of the total volume. They transport oxygen from the lungs to the body’s tissues using the protein hemoglobin, which also gives blood its red color.
Plasma is the pale yellow, liquid matrix, constituting about 55% of the total volume. It is mostly water but carries proteins, clotting factors, hormones, and nutrients.
White blood cells (leukocytes) are the immune system’s defense mechanism, fighting off infections and foreign invaders. Platelets (thrombocytes) are small cell fragments that play a primary role in hemostasis, the process of stopping bleeding. They interact with plasma clotting factors to form a plug at the site of injury. White blood cells and platelets together make up less than 1% of the total blood volume.
Separating Whole Blood into Usable Products
Whole blood is rarely transfused directly, usually only for massive hemorrhage where a patient needs all components immediately. Instead, the blood pack contents are separated into individual components for targeted therapy. This maximizes the use of a single donation, allowing one unit to potentially help several patients.
Separation is achieved through centrifugation, where the blood pack is rapidly spun in a specialized refrigerated machine. Centrifugal force causes the components to separate into layers based on density. Technicians then extract the distinct products into attached satellite bags within the sterile system.
The main product derived is Packed Red Blood Cells (PRBCs), used to restore oxygen-carrying capacity in patients with anemia or significant blood loss. Fresh Frozen Plasma (FFP) is rapidly frozen, preserving clotting factors needed to treat bleeding disorders or reverse the effects of certain medications.
Platelet concentrates are also prepared, often requiring pooling of products or collection via apheresis, to provide a therapeutic dose for patients with low platelet counts. White blood cells are generally removed, or reduced, from the final transfusion products through leukoreduction. This step is performed to minimize the risk of certain transfusion reactions and disease transmission, such as the transfer of cytomegalovirus (CMV). The result is a highly efficient system that provides specific, concentrated blood products tailored to the patient’s medical requirement.
Storage, Shelf Life, and Safety
Because each blood component has a unique biological makeup, they require vastly different conditions for safe storage and have varying shelf lives. Packed Red Blood Cells (PRBCs) must be refrigerated between 1°C and 6°C to maintain viability, giving them a shelf life of up to 42 days from collection. This relatively long window helps blood banks manage inventory.
Platelets are stored at room temperature (20°C to 24°C) and must be kept under continuous, gentle agitation to prevent clumping. This warm environment means platelets have the shortest shelf life, typically expiring in 5 to 7 days. Fresh Frozen Plasma (FFP) is stored in a freezer below \(-18^{\circ}\text{C}\), maintaining the integrity of its coagulation factors for up to one year.
Before any component is released for transfusion, it undergoes mandatory safety screening. All donated blood is tested for markers of infectious diseases, including Hepatitis B and C, and Human Immunodeficiency Virus (HIV). This multi-layered screening process ensures the blood product is safe for patient use.
The entire system, from collection to transfusion, is governed by strict controls. Bacterial contamination is a particular concern for platelets due to their room-temperature storage, requiring specific risk control strategies. The stringent requirements for storage and testing allow transfusion medicine to remain a reliable and life-saving intervention.