Assessment of toxoplasma IgG avidity test results in pregnant women.

nfection brought about by Toxoplasma gondii (T. gondii), toxoplasmosis, is transmitted to the fetus via the placenta. Infection may progress in the expectant mother totally asymptomatically. However, such infections are particularly significant because of undesired consequences for the fetus. Immunoglobulin G (IgG) avidity tests, which have come into use in recent years, make it possible to discriminate reliably between primary acute infections and reactivations, reinfections, or both, with a single serum sample. This discrimination has clinical value, particularly in pregnant women and immunosuppressive patients. Because appropriate use is not generally made of standard procedures and the time periods required by these in the immunoserological diagnosis of many infective illnesses, numerous difficulties are encountered in diagnosis and treatment. In general, the titration of different antibodies, and increases in the titer, are considered significant in immunoserological diagnosis. The determination of this requires a large amount of time. In the present study, IgG avidity tests, which have recently gained currency, will be taken into consideration and compared with classic methods in terms of optimal usage and early treatment.1 Sera from 879 women in the third trimester of pregnancy who attended the Obstetrics and Gynecology policlinic of the Dicle University Faculty of Medicine between 9 April 2002 and 9 May 2003 were evaluated for Toxoplasma IgG and IgM by the classic enzyme linked immunosorbent assay (ELISA) technique (Cobas Core II, Roche, USA). In patients determined to be positive for IgM, the same test was repeated the following week with new serum samples. Sera testing positive for both IgM and IgG and sera testing positive for IgG alone were stored at -20°C. Avidity tests (IgG avidity EIA Well; Radim, Italy) were performed with commercial kits. Results were interpreted as follows: avidity of greater than 30% was considered to be high, 20-30% was considered medium (gray region), and below 20% was considered low. A total of 879 serum samples taken from pregnant women in their third trimester were evaluated for Toxoplasma IgM and IgG by the classic ELISA technique. Of these sera, 21 (3.1%) tested positive for Toxoplasma IgM and IgG, and 305 (45.0%) for IgG alone. In patients found positive for both Toxoplasma IgM and IgG, the I ELISA test was repeated the following week with new serum samples, and the same results were obtained. All sera positive for both IgM and IgG, and as many of those positive for IgG alone as permitted by the number of kits, were analyzed by the IgG avidity test. In the evaluation of T. gondii avidity test results (Table 1), it was determined that 12 of the 21 patients testing positive for both IgM and IgG had a low avidity index (AI) (<20%), 6 had a medium AI (20-30%), and 3 had a high AI (>30%), and that only one of the patients testing positive for IgG alone had a low AI while the remaining 156 had high AIs. While primary Toxoplasma infections occurring in the first trimester of pregnancy may lead to severe malformations, this risk is minimal or nonexistent in infections occurring through reinfection, reactivation, or both. Hernanadez et al2 used the Vidas system to confirm positive results for IgM with ELISA in 89 serum samples collected from 1999 to 2002 in 20 patients suspected of toxoplasmosis. The IgG avidity was determined by the Liaison system. It was found that the sera taken from all but 9 of 20 IgM-positive patients had high IgG avidity, demonstrating the importance of the IgG avidity in excluding acute toxoplasmosis. Basiak et al3 tested 58 women with nodular toxoplasmosis and 34 women diagnosed with asymptomatic T. gondii infection for T. gondii antibodies at different times after the onset of infection using immunofluorescence assay (IFA), ELISA IgM, ELISA IgA, and IgG avidity tests. They determined that IFA had 76.2% sensitivity and 31-67% specificity, and that IgG avidity had 100% sensitivity and 41.7% specificity. It was found that all methods evaluated had only a limited value in the