69504 Diagnostic Pathology - IgM IgG antibodies Pg1.14

IgM antibodies are large due to their pentamer structure and therefore they bind directly to their corresponding antigen and can agglutinate RBCs in saline at room temperature.

IgG antibodies are small due to their monomeric structure and therefore are termed non-agglutinating, or incomplete antibodies. IgG antibodies are too small to directly agglutinate sensitised RBCs.

Sensitised RBCs are those coated with IgG antibodies as described previously. In order for agglutination to occur, these RBCs must be incubated with an antibody that will bind to the IgG antibodies creating a bridge with each one, linking the RBCs together. The antibody used is an Anti-Human Globulin (AHG) reagent which reacts with the Fc portion of IgG antibody, or the C3b/C3d component of Complement.