Elecsys® Toxo IgG Avidity

Immunoassay for the qualitative determination of T. gondii IgG avidity

Elecsys® Toxo IgG Avidity

Immunoassay for the qualitative determination of Toxoplasma gondii IgG avidity

Toxoplasmosis is a common infection caused by the protozoan Toxoplasma gondii (T. gondii).1 Healthy individuals generally have mild or no symptoms, however, if primary infection occurs during pregnancy, it can result in severe damage to the fetus.1

The risk of fetal damage is highest when the infection is acquired early in pregnancy, while the risk of transmitting the infection increases if the infection is acquired later in the pregnancy.1 Early treatment in acute infection during pregnancy can prevent or ameliorate congenital damage1.

The diagnosis of T. gondii infection starts with the detection of anti-Toxoplasma IgG and IgM antibodies. Toxoplasma IgG avidity test is performed to date the infection. The antibodies produced during the primary response have a lower avidity than those produced during the non-primary response, hence a high avidity early in gestation suggests that infection has taken place more than 4 months ago and rules out a recent primary acute infection.2 However, no clinical interpretation can be deduced from a low or grey-zone avidity result2.

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Elecsys® Toxo IgG Avidity

Elecsys® Toxo IgG Avidity

  • Systems

    cobas e 411 analyzer, cobas e 601 / cobas e 602 modules, cobas e 801 module

  • Testing Time

    cobas e 411 analyzer, cobas e 601 / cobas e 602 modules: 10 minutes pre-incubation + 18 minutes 
    cobas e 801 module: 27 minutes    

  • Test principle

    One-step double-antigen sandwich immunoassay under various buffer conditions

  • Calibration

    2-point

  • Interpretation

    <70 Avi % = low avidity
    70 – 79 Avi % = gray zone
    ≥80 Avi % = high avidity    

  • Traceability

    3rd International Standard for anti-toxoplasma serum (TOXM); NIBSC 

  • Sample material

    cobas e 411 analyzer, cobas e 601 / cobas e 602 modules: Serum collected using standard sampling tubes or tubes containing separating gel. Li‑heparin, K2‑EDTA, K3‑EDTA and Na‑citrate plasma.

     

    cobas e 801 module: Serum collected using standard sampling tubes or tubes containing separating gel. Li‑heparin, K2‑EDTA, K3‑EDTA and Na‑citrate plasma. Plasma tubes containing separating gel can be used.    

  • Sample volume

    2 x 10 μL cobas e 411 analyzer, cobas e 601 / cobas e 602 modules
    2 x 18 μL cobas e 801 module

  • Onboard stability

    14 days for cobas e 411 analyzer, cobas e 601 / cobas e 602 modules
    16 weeks for cobas e 801 module

  • cobas e flow

    cobas e 801 module: Automatic dilution, preparation of avidity and reference sample, and calculation of the avidity (Avi%)                   

  • Intermediate precision in positive samples

    cobas e 411 analyzer: CV 0.6 – 7.3 % 
    cobas e 601 / 602 modules: CV 0.0 – 8.7 %   
    cobas e 801 module: CV 0.4 – 5.4 % 

  • Diagnostic performance

    None of samples taken <4 months from onset of infection showed a high avidity result with Elecsys® Toxo IgG avidity assay    

References

 

  1. Montoya, J.G. et. al. (2004). Lancet 363, 1965-1976.
  2. Remington, J.S. et al. (2006). Infectious Diseases of the Fetus and Newborn Infant (Sixth Edition). Philadelphia: W.B. Saunders, 947-1091.