Difference between Affinity and Avidity

The binding of antigens and antibodies has been described in binding strength terms called affinity and avidity. The binding of antigen and antibody is a reversible process, and is known as agglutination.

What is Affinity?

Affinity is the binding strength between an antigen-binding site at the antibody and an antigen. It is the net result of attractive and repulsive forces between an antigen-antibody interaction. It is the degree of association between an antigen epitope and a paratope or antigen-binding site on an antibody.

What is Avidity?

Avidity is the cumulative strength required for the interaction between a multivalent antibody and a multimeric antigen. It is a collection of affinities but holds a larger value than all the affinities combined.

Affinity vs Avidity



Affinity is the strength required for an interaction between a site of antigen binding at an antibody and an antigen epitope. Avidity is the total strength required for the interaction between a multivalent antibody and multiple antigenic epitopes.
It is the strength between a single antigen-binding site on an antibody and an epitope of an antigen. It is the total binding strength between multimeric antigen-antibody reactions.
It is a balance between attractive and repulsive forces. It is larger than the sum of all affinities combined.

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Frequently Asked Questions


What is the difference between antigen affinity and avidity?

Affinity is the interaction between a single antigen binding site at the antibody and an antigen epitope, whereas avidity is the total strength of interaction between a multimeric antigen and a multivalent antibody.


What are the applications of avidity?

The avidity test for rubella, HIV, hepatitis and Epstein-Barr Virus (EBV) can be used to detect acute, recurrent or past infections by checking the avidity of IgG.


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