Description
Intended Uses: ELISA classic Toxoplasma gondii IgG and IgM tests are quantitative and qualitative immunoassays for the detection of human antibodies in serum or plasma directed against Toxoplasma gondii. The assays are recommended to determine the immune status and to differentiate acute from recent infections. The ELISA classic Toxoplasma gondii IgM test is the initial assay for the detection of acute infections. IgM antibodies directed against Toxoplasma gondii might persist over a long time period. ELISA classic Toxoplasma gondii IgG test in combination with ELISA classic Toxoplasma gondii avidity reagent (Order No.: B110AVID) allows the determination of IgG antibody avidity for the differentiation of acute from recent infections. ELISA classic Toxoplasma gondii IgM test is suitable for newborn screening with dried blood spots (DBS).
Principle of the Assay: To determine the performance characteristics of the ELISA classic Toxoplasma gondii IgG test, an external comparison study, utilizing sera from 450 patients and healthy individuals, was performed in parallel with an indirect immunofluorescence test. The results indicate a sensitivity of 98.2 % and specificity of 99.4 %. An internal study was also carried out using sera from 1000 pregnant women. An indirect immunofluorescence test was also used as the reference test and discrepant results were further tested in the Sabin-Feldman-Test to determine their true status. The results indicate a sensitivity of 97.8 % and specificity of 99.8 %. An external study, to determine the sensitivity and specificity of the ELISA classic Toxoplasma gondii IgM test, utilizing a total of 256 sera, of which 104 were positive, was carried out using two commercially available IgM tests as comparison ( from company A and company B). The positive IgM sera were selected using the Toxoplasma IgM test from company A. The use of a borderline region between 450 and 540 U/ml resulted in 19 positive sera not returning a positive result, seven of which were potentially from acute infections. In this evaluation the ELISA classic Toxoplasma gondii IgM test demonstrated a higher sensitivity than the test from company B which had returned negative test results for 28 of the 104 positive. Using the 450 and 540 U/ml borderline region the ELISA classic test when compared to that from company A returned a specificity of 98.6 %. Using a borderline region between 300 and 350 U/ml resulted in eleven positive sera not being recognized. Taking the results of further testing and the patients’ clinical background into account, only two of these discrepant sera were from possibly primary infections and the remaining 9 were the result of persisting IgM or unspecific IgM. In relation to diagnostically relevant primary infections a sensitivity of 97.8 % was calculated. A specificity of 95.7 % was determined in comparison to the ELISA from company A. classic Toxoplasma gondii IgM test to be attained when using the 300 to 350 U/ml borderline region. In an internal performance study to determine the sensitivity of the Toxoplasma gondii IgM a serum panel of 86 sera (29 of which were positive for IgM) was tested in the test and a further 2 commercially available IgM ELISA tests (company C and company B). the positive IgM sera were selected using the test from company C. Using a borderline region from 450 to 540 U/ml, five positive sera were not recognized so giving a sensitivity compared to the test from company C of 82.8 %. Compared to the test from company B the test recorded 100% sensitivity. To determine the specificity 372 sera from pregnant women and blood donors were investigated. Using the same borderline region from 450 to 540 U/ml a specificity of 98.9 % compared to the test from company B was attained. Performance Characteristics (external studies) Sensitivity Specificity ELISA classic Toxoplasma gondii IgG 98.2 % 99.4 % ELISA classic Toxoplasma gondii IgM 97.8 % 95.7 % Borderline results were not included in the calculations. ELISA classic Toxoplasma gondii IgG test is suitable for the determination of immune status in pregnant women. Hemoglobin levels of up to 10 mg/ml in serum had no effect on the results obtained. Investigation of a serum panel with antibody activities against potentially cross-reacting parameters (sera with auto-antibodies, rheumatoid factor, EBV and syphilis sera) did not reveal any evidence of false positive results due to cross-reactions. Infection with Epstein-Barr-Virus may lead to a polyclonal stimulation of antibody production and so lead to false positive Toxoplasma gondii IgM antibody results. In addition it should be noted that Toxoplasma gondii igM antibodies may persist for months or even years after an infection has resolved