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Evaluation of enzygnost IgA conjugate in combination with the kit Enzygnost Toxoplasmosis IgG (Siemens Healthcare Diagnostics) for the detection of IgA anti-Toxoplasma gondii in human serum samples

Abstract number: P711

Marangoni A., Moroni A., Accardo S., Cevenini R.

Objectives: Laboratory diagnosis of Toxoplasmosis is mainly based on serological methods, particularly important in the most challenging situations, as diagnosis of primary infection during pregnancy and diagnosis of congenital infection. Tests for the detection of IgA antibodies are especially important in the newborns, because they are more sensitive than IgM conventional methods. The purpose of this study was to evaluate diagnostic performances of Enzygnost system for IgA detection, achieved by using Enzygnost Anti-human IgA/POD Conjugate in combination with Enzygnost Toxoplasmosis IgG (Siemens Healthcare Diagnostics Products GmbH, Marburg, Germany).

Methods: A retrospective study was performed with 591 serum samples submitted to the Microbiology Laboratory of S. Orsola Hospital in Bologna for Toxoplasmosis screening. All the sera were tested by Enzygnost Toxoplasmosis IgG, Enzygnost Toxoplasmosis IgM and Enzygnost system for IgA (Siemens Healthcare Diagnostics). Border-Line or positive IgM results were confirmed by Vidas Toxo IgM (bioMerieux, Marcy l'Etoile, France). Finally, IgG Avidity was performed by Vidas Toxo IgG Avidity (bioMerieux, Marcy l'Etoile, France) and LDBio Toxoplasma WB IgG/IgM (LDBio Diagnostics, Lyon, France).

Moreover, a second study was performed with 172 selected sera in order to compare results obtained by Enzygnost system for IgA with those obtained by Enzywell Toxoplasma IgA (Diesse, Monteriggioni, Siena, Italy).

Results: Retrospective study. 453/591 samples were negative, 53 were Border-Line and 85 were positive when tested by Enzygnost system for IgA. 3 babies were correctly diagnosed as infected infants because of the presence of IgA antibodies at birth. These newborns had negative IgM results in both conventional methods used, whereas comparative WB confirmed the infection because of the different immunological profiles between maternal and newborn samples.

Comparative study. Results obtained by the two methods are summarised in Table 1. They showed a concordance of 93%.

Conclusion: Enzygnost system for IgA anti-Toxoplasma showed very good diagnostic performances: in the retrospective study it allowed the correct identification of three infected newborns and in the comparative study it showed a higher specificity than Enzywell Toxoplasma IgA, since no sera from healthy blood donors were scored reactive. We conclude that its good performances and its suitability for automation make it an ideal screening test.

Table 1. Enzygnost system for IgA anti-Toxoplasma and Enzywell Toxoplasma IgA reactivities in relation to the four groups of subjects tested for the comparative study

Study groupaNo. of samplesNumber of reactive samples when tested by Enzygnost and Enzywell, respectively (%)% Concordance
  + and +- and -+ and -- and + 
Pregnant women5741 (71.3)8 (14.0)7 (12.3)1 (1.8)86.0
Infants320 (0)32 (100)0 (0)0 (0)100
HIV positive263 (11.5)22 (84.6)0 (0)1 (3.8)96.2
Healthy blood donors570 (0)54 (94.7)0 (0)3 (5.3)94.7
Total17244 (25.6)116 (67.4)7 (4.1)5 (2.3)93.0
aImmunological situation of the patients:
• All the pregnant women had low Avidity and IgM positive results;
• No infants born to mothers with primary infection during their pregnancies were infected by Congenital Toxoplasmosis (all of them turned to be seronegative within 1 year of age);
• All HIV positive patients had positive IgG results. The 3 patients with IgA positive results by both methods were also IgM positive;
• The healthy blood donors were selected to be IgG and IgM seronegative for Toxoplasmosis.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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