Evaluation of a New Immunochromatography Technology Test (LDBio Diagnostics) To Detect Toxoplasma IgG and IgM: Comparison with the Routine Architect Technique

Abstract

A study comparing the ICT (immunochromatography technology) Toxoplasma IgG and IgM rapid diagnostic test (LDBio Diagnostics, France) with a fully automated system, Architect, was performed on samples from university hospitals of Marseille and Saint-Etienne. A total of 767 prospective sera and 235 selected sera were collected. The panels were selected to test various IgG and IgM parameters. The reference technique, Toxoplasma IgGII Western blot analysis (LDBio Diagnostics), was used to confirm the IgG results, and commercial kits Platelia Toxo IgM (Bio-Rad) and Toxo-ISAgA (bioMérieux) were used in Saint-Etienne and Marseille, respectively, as the IgM reference techniques. Sensitivity and specificity of the ICT and the Architect IgG assays were compared using a prospective panel. Sensitivity was 100% for the ICT test and 92.1% for Architect (cutoff at 1.6 IU/ml). The low-IgG-titer serum results confirmed that ICT sensitivity was superior to that of Architect. Specificity was 98.7% (ICT) and 99.8% (Architect IgG). The ICT test is also useful for detecting IgM without IgG and is both sensitive (100%) and specific (100%), as it can distinguish nonspecific IgM from specific Toxoplasma IgM. In comparison, IgM sensitivity and specificity on Architect are 96.1% and 99.6%, respectively (cutoff at 0.5 arbitrary units [AU]/ml). To conclude, this new test overcomes the limitations of automated screening techniques, which are not sensitive enough for IgG and lack specificity for IgM (rare IgM false-positive cases).

Keywords: Architect; Toxoplasma gondii; immunochromatography test; immunoglobulin G; immunoglobulin M; serology; toxoplasmosis.

FIG 1

Distribution of nonselected IgG serum titers with Architect. The dark columns correspond to sera that are positive by ICT IgG-IgM (LDBIO Diagnostics). The gray columns correspond to sera that are negative by ICT IgG-IgM (LDBIO Diagnostics).

FIG 2

Toxoplasma IgGII Western blot (LDBIO Diagnostics) profiles. These profiles were obtained from 11 sera of the panel corresponding to nonspecific IgG on Architect with a negative ICT. C, control; C1, positive control with IgG of 5 UI/ml on Architect; C2, positive control with IgG of 1.2 UI/ml on Architect; C3, positive control of a confirmed seroconversion with IgG of 0.6 UI/ml on Architect; P, panel. Eleven sera were used: P1, IgG of 3.2 UI/ml on Architect, negative ICT, 2 bands (i.e., negative) with Toxo II IgG Western blot analysis; P2 to P4, IgG of 3.2 to 21.6 UI/ml on Architect, negative ICT, 1 band (i.e., negative) with Toxo II IgG Western blot analysis; P5 to P11, IgG of 3.8 to 6.7 UI/ml on Architect, negative ICT, 0 band (i.e., negative) with Toxo II IgG Western blot analysis; P6 to P10, not presented.