Blood transfusions are a medical procedure that can be life-saving for individuals who have experienced significant blood loss or have conditions affecting their blood components. For a transfusion to be successful and safe, ensuring the compatibility between the donor’s blood and the recipient’s blood is of utmost importance.
Understanding Blood Types
Blood types are determined by specific protein molecules, called antigens, found on red blood cells, and corresponding antibodies in blood plasma. The two most significant systems for blood transfusions are the ABO and Rh systems. In the ABO system, individuals can have A antigens (Type A blood), B antigens (Type B blood), both A and B antigens (Type AB blood), or neither (Type O blood) on their red blood cells. Plasma contains pre-formed antibodies against antigens not present on one’s own red blood cells; for example, Type A blood has anti-B antibodies.
The Rh system determines whether blood is positive or negative, based on the presence or absence of the RhD antigen. Unlike ABO antibodies, Rh antibodies are typically only produced after exposure to Rh-incompatible blood, such as during a transfusion or pregnancy. These antigens and antibodies act as markers the immune system uses to identify self from non-self.
The Immune Response to Incompatible Blood
When a person receives an incompatible blood type, their immune system recognizes foreign antigens on the donor red blood cells as a threat. Pre-existing antibodies in the recipient’s plasma bind to these antigens, triggering an acute hemolytic transfusion reaction (AHTR). This binding activates the complement system, a part of the immune defense, which leads to the rapid destruction of transfused red blood cells.
Hemolysis releases free hemoglobin into the bloodstream. This immune activation also triggers a systemic inflammatory response, leading to the release of various inflammatory substances and the activation of the body’s clotting cascades.
Factors Influencing Severity and Outcome
Even a small amount of incompatible blood can trigger a severe reaction. The severity of the reaction correlates with the volume of incompatible blood transfused. The destruction of red blood cells leads to the release of free hemoglobin, which can cause acute kidney injury.
The systemic inflammatory response can also lead to disseminated intravascular coagulation (DIC), a condition where widespread clotting consumes clotting factors, followed by uncontrolled bleeding. Patients may experience shock and multi-organ failure.
Ensuring Transfusion Safety
To prevent incompatible transfusions, safety protocols are in place before any blood product is administered. These measures begin with blood typing of both the donor and the recipient to determine their ABO and Rh types. An antibody screen is then performed on the recipient’s blood to detect any unexpected antibodies.
Cross-matching is a final step, where donor red blood cells are mixed with recipient plasma to observe for immune reactions. Patient identification protocols are followed at every stage to ensure the right patient receives the correct blood product. Due to these safety measures, severe incompatible transfusion reactions are rare.