Evaluation of the TGS TA system for the detection of anti-Toxoplasma antibodies

Background and aims. The aim of the present study was to evaluate the new chemiluminescence TGS TA system of Technogenetics (Milan, Italy) for detecting anti-Toxoplasma IgG and IgM antibodies and IgG avidity. The TGS TA system was compared with our chemiluminescence routinely used system, LIAISON XL, supplied by Diasorin (Saluggia, Italy), for the detection of IgG and IgM antibodies. Only in positive IgM samples (retrospective study) and for the IgG avidity (if existent), TGS TA system was compared to an Enzyme Linked Fluorescent Assay (ELFA) test (VIDAS, BioMérieux, Marcy-l’Étoile, France).
Materials and methods. Three hundred and one sera samples, from women who came to our centre for the routine follow up pregnancy, were examined with the TGS TA system and divided in 3 groups according to IgG and IgM screening LIAISON XL tests: 106 were non-immune women (Group 1), 100 were pregnant with past infection (Group 2) and 95 were pregnant with positive or equivocal IgM (82 with positive IgG and 13 with negative IgG) (Group 3).
Results. The overall concordance of the IgG results between LIAISON XL and TGS TA was 99.3%: 100% in Group 1, 98% in Group 2 and 100% in Group 3. The overall concordance of the IgM results between LIAISON XL and TGS TA was 93.9%: 100% in Group 1, 94% in Group 2 and 82.8% in Group 3. In Group 3, the concordance between the results of the IgG avidity with the ELFA and TGS TA tests was 81.7%. Comparing the clinical diagnosis obtained with our protocol and that of the TGS TA system, the overall concordance was 92.7%: 100% in Group 1, 92.0% in Group 2 and 78.9% in Group 3.
Conclusions. The overall concordance of IgG antibodies is excellent for both protocols while for IgM antibodies is very high in the first group and lower in the third group, due to the presence of non-specific IgM subjects in this group. The TGS TA avidity test seems to predict ealier the maturation of the IgG compared to the ELFA test since many samples with low avidity with the ELFA were seen with moderate avidity with TGS TA and all those with borderline avidity with the ELFA were seen with high avidity with TGS TA. This system shows to be a valuable tool with overall good clinical correlation and able to clearly identify nonspecific subjects, those with a non-recent infection.