A blood transfusion is a standard medical procedure that involves transferring donated blood products into a patient’s circulatory system intravenously. This intervention becomes necessary when a person has lost a significant volume of blood due to trauma or surgery, or when their body cannot produce enough of a specific blood component. Modern medicine rarely uses whole blood, instead relying on component therapy, which allows a single donation to help multiple patients by separating the blood into its distinct parts.
The Primary Components of Transfused Blood
The most common component is packed Red Blood Cells (RBCs), which are responsible for transporting oxygen from the lungs to the body’s tissues and removing carbon dioxide. These cells contain hemoglobin, the iron-rich protein that binds to oxygen, and are often transfused to patients suffering from severe anemia or those with significant blood loss to restore oxygen-carrying capacity.
Plasma is the yellowish liquid portion of blood, primarily composed of water, proteins, and clotting factors. Transfused as Fresh Frozen Plasma (FFP) after separation and freezing, it is used to replace missing clotting factors in patients with liver failure, certain bleeding disorders, or those experiencing massive hemorrhage. The antibodies and other proteins within the plasma also play a role in fighting infection and maintaining blood pressure.
Platelets are small, colorless cell fragments that circulate in the blood and are essential for stopping bleeding. They achieve this by aggregating together to form a temporary plug at the site of a damaged blood vessel, initiating the blood clotting process. Platelet transfusions are typically given to patients with low platelet counts (thrombocytopenia), often resulting from chemotherapy or bone marrow failure, to prevent or control serious bleeding.
A distinct component derived from plasma is Cryoprecipitate, a concentrated source of specific clotting proteins. This product is made by thawing fresh frozen plasma at a low temperature and collecting the cold-insoluble precipitate that forms. Cryoprecipitate is rich in fibrinogen, Factor VIII, Factor XIII, and von Willebrand factor, and it is primarily administered to patients with low fibrinogen levels, such as those with massive trauma or disseminated intravascular coagulation.
Processing and Storage of Blood Products
Once blood is donated, it must be separated into its individual components. Whole blood is first placed into a centrifuge, a machine that spins the blood at high speeds, which separates the mixture into layers based on density. This process yields the separate components: Red Blood Cells settle at the bottom, a buffy coat containing white blood cells and platelets forms in the middle, and plasma remains at the top.
Packed Red Blood Cells are stored in specialized refrigerators at a temperature range of 1°C to 6°C, often with preservative solutions that allow them to be stored for up to 42 days. Platelets, conversely, must be stored at room temperature, and they require continuous gentle agitation to prevent them from clumping together and losing their function, giving them a shelf life of only five to seven days.
Fresh Frozen Plasma is flash-frozen at temperatures below -18°C shortly after collection to preserve the activity of the unstable clotting factors. This deep-freezing allows plasma to be stored for up to a year, but it must be thawed carefully just before transfusion. Cryoprecipitate is also stored frozen at or below -18°C, but once thawed, it must be used quickly, typically within four to six hours.
Determining Blood Compatibility
Before any blood product is administered, a series of laboratory tests is performed to ensure the donor’s blood is compatible with the recipient’s. The foundation of compatibility is the ABO blood group system, which classifies blood based on the presence or absence of A and B antigens on the surface of red blood cells. A person’s plasma naturally contains antibodies against the antigens they lack, meaning an incompatible transfusion would cause the recipient’s antibodies to attack and destroy the donor’s red cells.
The Rh factor is the second most important system, determined by the presence or absence of the Rh D antigen, which classifies blood as positive or negative. Rh-negative individuals do not naturally have antibodies against the Rh D antigen, but exposure to Rh-positive blood can cause them to develop these antibodies, putting them at risk for a future reaction. Therefore, Rh-negative patients should ideally receive Rh-negative blood products, especially red blood cells.
The final confirmation of compatibility is achieved through a procedure called cross-matching. For a major cross-match, a sample of the recipient’s serum or plasma is mixed with a sample of the donor’s red blood cells. If clumping, or agglutination, occurs, the blood is incompatible and cannot be used for the transfusion.
An antibody screen is also performed to check for other, less common antibodies in the recipient’s blood that might react with the donor’s cells, even if the ABO and Rh types match. This screening ensures the safety of the transfusion.