What is agglutination and how is it used to differentiate blood type?

Agglutination is defined as the clumping of blood particles which occurs when an antigen binds with corresponding antibody in blood plasma.

Agglutination is most commonly used in blood grouping. While determining blood type, few blood drops are mix with sera that contain antibodies (anti-sera) against the ABO and the Rh systems. If the blood cells forms clump, the antibody bound to appropriate antigen on the cells and on the basis of agglutination blood group is assigned to an individual, for example if blood agglutinates in anti-A, the A antigen and are Type A blood group.