Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 29.10.2020

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Avidity (from Latin avidus, "greedy") refers to the strength of the antigen-antibody binding after the formation of the antigen-antibody complex. Avidity is composed of the number of binding sites and their affinity (antibody valence). It is not relevant whether the binding is specific or multispecific. It is multi-specific if an antibody reacts with different antigenic determinants(cross-reactivity).

The determination of avidity is important for the clarification of diagnostically ambiguous cases, such as reactivations, persistent IgM-AK, polyclonal stimulation. (Prince HE et al. 2014)

Monovalent interactions have a low avidity, bivalent ones a high avidity and polyvalent ones a very high avidity. Low-avidity antibodies are present when the ELISA absorbance is significantly reduced by urea treatment. The relative avidity index (RAI) is calculated from the measured values with and without urea treatment.

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  1. Prince HE et al (2014) Role of cytomegalovirus (CMV) IgG avidity testing in diagnosing primary CMV infection during pregnancy. Clin Vaccine Immunol 21:1377-1384.
  2. Suligoi B et al (2017) HIV avidity index performance using a modified fourth-generation immunoassay to detect recent HIV infections. Clin Chem Lab Med 55:2010-2019.

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Last updated on: 29.10.2020