Effect of Testing for IgG Avidity in the Diagnosis ofToxoplasma gondiiInfection in Pregnant Women: Experience in a US Reference Laboratory

Abstract

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.

Prevalence of acute toxoplasmosis infection among 41,112 pregnant women and the mother-to-child transmission rate in a public hospital in South Brazil

“…The introduction of the IgG avidity test in the diagnostic panel of acute toxoplasmosis reduced false-positive rates and unnecessary diagnostic and therapeutic interventions (Liesenfeld et al 2001, Montoya et al 2002, Remington et al 2004.…”

Management of the Toxoplasmosis in Pregnancy: Knowledge and Attitude of Physicians

“…Aviditenin yüksek olması infeksiyonun 12 hafta ve öncesinde geçirildiğini gösterir. İlk trimestırda infeksiyonun değerlendi-rilmesinde avidite testinin önemi büyüktür [19,20] . Çalışmamızda yüksek aviditenin anlamı hekimlerin %79'u tarafından doğru cevaplanmıştır.…”

Kinetics and time dependence of the differential agglutination of acetone [AC]- and formalin [HS]-fixed Toxoplasma tachyzoites by serum of mice with experimental toxoplasmosis

“…2.5 ml of PBS containing 0.2 M 2-mercaptoethanol) then followed as twofold sera dilutions. The serum dilution for HS antigen (1:2,000) was assigned an antibody titer of 100 IU/ml (Dannemann et al 1990;Liesenfeld et al 2001;Montoya et al 2007). Sera that were negative in the conventional direct agglutination test were not evaluable in the AC/HS test.…”

“…Twofold dilutions of sera were done starting with 1:100. The serum dilution for AC antigen (1:100) was assigned an antibody titer of 50 IU/ml (Dannemann et al 1990;Liesenfeld et al 2001;Montoya et al 2007). Thus, an AC test titre of \50 IU/ml was considered in sera positive in conventional agglutination test and negative in the AC test.…”

“…The differential agglutination of acetone [AC]-fixed versus that of formalin [HS]-fixed tachyzoites is used in the differential agglutination (AC/HS test) a serological test that compares the titers obtained with Formalin-fixed tachyzoites (HS antigen) with those obtained with acetone-or methanol-fixed tachyzoites (AC antigen) (Montoya et al 2007). The test was used to diagnose toxoplasmic encephalitis in AIDS patients (Suzuki et al 1988) and toxoplasmic lymphadentitis (Montoya et al 2007) and is one of a group of tests forming Toxoplasma serum profile (Kaul et al 2004) including a double sandwich IgM ELISA and the Sabin-Feldman dye test in combination with IgG avidity results to distinguish between recently acquired and distant infections in pregnant females (Liesenfeld et al 2001;Remington et al 2006). Results of the differential agglutination test are recorded as acute or non-acute patterns (Montoya et al 2007).…”