What is the role of immunoglobulin G (IgG) avidity testing in the diagnosis of toxoplasmosis?

Updated: Mar 08, 2019
  • Author: Murat Hökelek, MD, PhD; Chief Editor: Michael Stuart Bronze, MD  more...
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The results of the IgG avidity test may help to differentiate patients with acute infection from those with chronic infection better than do alternative assays, such as assays that measure IgM antibodies. As is true for IgM antibody tests, the avidity test is most useful when performed early in gestation.

IgG produced early in infection is less avid and binds to T gondii antigens more weakly than do antibodies produced later in the course of infection. High antibody avidity indicates an older, earlier infection. This test may be helpful in the setting of pregnancy, as the timing of infection has prognostic value. A long-term pattern occurring late in pregnancy does not exclude the possibility that the acute infection may have occurred during the first months of gestation. [51]

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