Anti-Toxoplasma IgG assays: What performances for what purpose? A systematic review

Abstract

Chronic infection with Toxoplasma gondii is attested by the detection of specific anti-Toxoplasma IgG. A wide panel of serologic methods is currently marketed, and the most suitable method should be chosen according to the laboratory resources and the screened population. This systematic review of evaluation studies aimed at establishing an overview of the performances, i.e. sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of marketed anti-Toxoplasma IgG assays, and discussing their technical characteristics to guide further choice for routine diagnostic use. According to PRISMA guidelines, the search performed in PubMed and Web of Science databases recovered 826 studies, of which 17 were ultimately included. Twenty commercial anti-Toxoplasma IgG assays were evaluated, in comparison with an accepted reference method. Most of them were enzyme-immunoassays (EIAs, n = 12), followed by agglutination tests (n = 4), immunochromatographic tests (n = 3), and a Western-Blot assay (WB, n = 1). The mean sensitivity of IgG assays ranged from 89.7% to 100% for standard titers and from 13.4% to 99.2% for low IgG titers. A few studies pointed out the ability of some methods, especially WB to detect IgG early after primary infection. The specificity of IgG assays was generally high, ranging from 91.3% to 100%; and higher than 99% for most EIA assays. The PPV was not a discriminant indicator among methods, whereas significant disparities (87.5%–100%) were reported among NPVs, a key-parameter assessing the ability to definitively rule out a Toxoplasma infection in patients at-risk for opportunistic infections.

Serological diagnosis of toxoplasmosis: evaluation of the commercial test recomLine Toxoplasma IgG immunoblot (Mikrogen) based on recombinant antigens

“…Thus, as already shown by Simon et al, we observed that reactivity against the GRA8 antigen led to falsepositive results [30]. Simon et al hypothesize that past contact with Neospora caninum and Hammondia hammondi, two parasites close to T. gondii, could explain false-positive results with ARCHITECT-IgG and IB-recomLine, mostly due to crossreaction with GRA8 (used by both ARCHITECT and IB-recomLine) and also GRA7 to a lesser extent (only used by IB-recomLine) [26]. Therefore, IB-recomLine could result in false-positive IgG detections and bias the determination of immune status.…”

“…Determining the immune status is essential in three main situations: pregnant women, immunocompromized patients and transplant recipients or donors [26]. For pregnant women, detection of specific IgG antibodies without IgM detection at the beginning of pregnancy indicates a past infection and rules out the risk of a congenital primary infection [21].…”

Toxoplasma gondii Infection Among Institutionalized Children with Down syndrome in Sana’a city, Yemen: Implications of Low IgG Seroprevalence

“…According to the manufacturer, the relative sensitivity of this immunoassay ranges from 99.5 to 100.0% [lower 95% confidence interval (CI): 97.6-99.1%], and the relative specificity of the immunoassay ranges from 98.8 to 100.0% [lower 95% confidence interval 95% CI: 96.8-99.2%] [13]. Moreover, a recent systematic review and meta-analysis of assays for detecting anti-Toxoplasma IgG revealed a mean sensitivity level of 98.6% (95% CI: 97.5-100), a mean specificity level of 99.6% (95% CI: 98.7-100), a mean positive predictive value of 99.2% (95% CI: 98.3-100) and a mean negative predictive value of 99.4% (95% CI: 98.7-100) for Elecsys® Toxo IgG assay, with 100% concordance with the dye test for sera with interfering diseases [14].…”

Modern Serological Diagnosis of Toxoplasmosis: Literature Review

“…Производительность этих тестов варьируется в достаточно широких пределах. Так, при сравнении 17 различных публикаций при исследовании на IgG к T. gondii чувствительность тестов составляла от 89,7% до 100%, а специфичность -от 91,3% до 100% [8].…”