Effect of testing for IgG avidity in the diagnosis of Toxoplasma gondii infection in pregnant women: experience in a US reference laboratory

J Infect Dis. 2001 Apr 15;183(8):1248-53. doi: 10.1086/319672. Epub 2001 Mar 16.


The usefulness of testing for IgG avidity in association with Toxoplasma gondii was evaluated in a US reference laboratory. European investigators have reported that high-avidity IgG toxoplasma antibodies exclude acute infection in the preceding 3 months. In this US study, 125 serum samples taken from 125 pregnant women in the first trimester were chosen retrospectively, because either the IgM or differential agglutination (AC/HS) test in the Toxoplasma serologic profile suggested or was equivocal for a recently acquired infection. Of 93 (74.4%) serum samples with either positive or equivocal results in the IgM ELISA, 52 (55.9%) had high-avidity antibodies, which suggests that the infection probably was acquired before gestation. Of 87 (69.6%) serum samples with an acute or equivocal result in the AC/HS test, 35 (40.2%) had high-avidity antibodies. Forty women were given spiramycin, to prevent congenital transmission, and 7 (17.5%) had high-avidity antibodies. These findings highlight the value of testing a single serum sample obtained in the first trimester of pregnancy for IgG avidity.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antibodies, Protozoan / blood*
  • Antibody Affinity
  • Enzyme-Linked Immunosorbent Assay / methods
  • Female
  • Hemagglutination Tests
  • Humans
  • Immunoglobulin E / blood
  • Immunoglobulin G / blood*
  • Immunoglobulin M / blood
  • Pregnancy
  • Pregnancy Complications, Parasitic / diagnosis*
  • Pregnancy Trimester, First
  • Reference Values
  • Reproducibility of Results
  • Retrospective Studies
  • Toxoplasma / immunology
  • Toxoplasmosis / diagnosis*
  • United States


  • Antibodies, Protozoan
  • Immunoglobulin G
  • Immunoglobulin M
  • Immunoglobulin E