Why agglutination takes place after blood transfusion?

Agglutination in a blood transfusion occurs when the red blood cells (RBCs) of the donor and recipient react, causing them to clump together. This reaction can be life-threatening if the RBCs are destroyed, leading to insufficient oxygen supply to the body's tissues and organs.

There are several reasons why agglutination may occur after a blood transfusion:

1. ABO blood group incompatibility: The ABO blood group system is determined by the presence or absence of specific antigens (A and B) on the surface of RBCs. Individuals can have type A, B, AB, or O blood, based on the antigens present in their blood. If a patient receives a blood transfusion from a donor with incompatible ABO blood type, the recipient's immune system will recognize the foreign antigens as foreign and produce antibodies against them. These antibodies will bind to the donor RBCs, causing agglutination. For example, if a person with type A blood receives a transfusion from a donor with type B blood, the recipient's anti-B antibodies will attack the donor's B antigens, leading to agglutination.

2. Rh factor incompatibility: The Rh factor is another important antigen present on RBCs. Individuals are either Rh-positive (Rh+) if they have the Rh antigen on their RBCs or Rh-negative (Rh-) if they lack the Rh antigen. A person with Rh-negative blood can develop antibodies against the Rh antigen if exposed to Rh-positive blood. If an Rh-negative recipient receives a transfusion from an Rh-positive donor, the recipient's immune system may produce anti-Rh antibodies, which can lead to agglutination of the donor's RBCs.

3. Minor blood group incompatibilities: In addition to the ABO and Rh blood group systems, there are many other minor blood group antigens. In some cases, individuals may have rare antigens on their RBCs that can be recognized as foreign by the recipient's immune system, leading to agglutination after transfusion.

To prevent agglutination and potential transfusion reactions, compatibility testing is performed before blood transfusions. This involves testing the recipient's blood for compatibility with potential donor blood. ABO blood group and Rh factor matching, along with additional compatibility tests, are essential to ensure safe blood transfusions and minimize the risk of complications.