Understanding an individual's blood group is a critical component of transfusion medicine. It ensures compatibility in blood transfusions, organ transplants, and even during pregnancy. Determining these blood groups involves the ABO and Rh blood typing systems, utilizing specific antigens and corresponding anti-sera to identify an individual's blood type.

Antigens are protein molecules that reside on the surface of red blood cells (RBCs). The ABO and Rh blood typing systems target antigens A, B, and D (Rh). These antigens serve as the foundation for blood grouping. The identification of these antigens involves a process known as agglutination.

Agglutination is a reaction that occurs when an antigen comes into contact with its corresponding antibody, causing the cells to clump together. In blood typing, this reaction is used to identify the presence of specific antigens by using anti-sera against them. There are three primary anti-sera used in this process:

1. Anti-A Serum: Used to test for the presence of antigen A.
2. Anti-B Serum: Used to identify antigen B.
3. Anti-D Serum: Applied to determine the presence of the Rh antigen.

The occurrence of agglutination upon the addition of these anti-sera indicates the presence of the corresponding antigen. For example, if agglutination occurs when anti-A serum is added, it signifies that the individual has blood type A. Similarly, if agglutination happens with anti-D serum, the individual is Rh-positive. If no agglutination occurs with any serums, the individual belongs to the O blood group and is Rh-negative.