The concepts of zeta potential and van der Waals forces help us understand how agglutination is achieved.
Zeta potential is defined as the degree of negative charge on the surface of a red blood cell; it is the potential difference between the negative charges on the red blood cells (RBCs) and the cations in the fluid portion of the blood. Larger zeta potential around the RBCs results in a decrease in the affinity between the antibody and antigen.
van der Waals forces are the attractive or repulsive forces between molecules. These forces play a crucial role in the strength of agglutination (avidity).