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The Antiglobulin test

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There are two major types of blood group antibodies, IgM andIgG.

Because of their large pentamer structure, IgM antibodies bind tocorresponding antigen and directly agglutinate RBCs suspendedin saline.

IgG antibodies are termed nonagglutinating because their

monomer structure is too small to agglutinate sensitized RBCsdirectly. The addition of AHG containing anti-IgG to RBCssensitized with IgG antibodies allows for hemagglutination ofthese sensitized cells.

Some blood group antibodies have the ability to bindcomplement to the RBC membrane.

Antiglobulin tests detect IgG and/or complement-sensitized RBCs.

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1. Antibody molecules and complementcomponents are globulins.

2. Injecting an animal with humanglobulin stimulates the animal to

produce antibody to the foreign protein(i.e., AHG). Serologic tests employ a

variety of AHG reagents reactive withvarious human globulins, including anti-IgG, antibody to the C3d component ofhuman complement,and polyspecific

reagents that contain both anti-IgG and

anti-C3d activity.

3. AHG reacts with human globulinmolecules, either bound to RBCs or free

in serum.

4. Washed RBCs coated with humanglobulin are agglutinated by AHG.