The antigens A, B, and Rh on the surface of red blood cells serve as the foundation for blood grouping. When these antigens come in contact with their corresponding antibody, it triggers a reaction known as agglutination, leading to the clumping of cells. This principle is used in blood typing to identify the type of antigens on the red blood cells using three specific anti-sera or antibody-containing solutions. Anti-A serum has antibodies against antigen A, while the anti-B serum has antibodies against antigen B. In addition, the anti-D serum is used to determine the presence of the Rh antigen. When an individual's blood group is to be determined, some blood drops of peripheral blood are mixed with the three anti-sera. If agglutination is observed with anti-A and anti-D serum, then it indicates that the individual has the A-positive blood type. On the other hand, if no agglutination occurs with any of the anti-sera, the individual belongs to the O blood group and is Rh-negative.