Comparison of the Vitek Immunodiagnostic Assay System with an indirect immunoassay (Toxostat Test Kit) for detection of immunoglobulin G antibodies to Toxoplasma gondii in clinical specimens

Abstract

The value and convenience of testing for specific anti-Toxoplasma gondii antibodies have led to the development of various antibody detection methods, such as the enzyme immunoassay. Two enzyme immunoassays, the Vitek Immuno-Diagnostic Assay System (VIDAS; Vitek Systems, Hazelwood, Mo.) and the Toxostat Test Kit (TST; Whittaker Bioproducts, Walkersville, Md.), were compared for their ability to detect T. gondii immunoglobulin G antibodies in fresh human sera. Specimens were tested according to the instructions of each manufacturer. Of 304 serum specimens tested, the results for 282 (93%) agreed in both assays (77 were positive and 205 were negative). The results for the remaining 22 (7%) specimens were discrepant; 20 of the 22 specimens tested low positive or equivocal by Toxostat and negative by VIDAS. Upon retesting, 8 of these 22 specimens were in concordance, increasing the level of agreement to 95.3%. Intra-assay reproducibility was tested with four to nine replicates of each of seven samples (four positive, one negative, and two equivocal) by both tests and six replicates of one standard by VIDAS. Coefficients of variation (CVs) for VIDAS were 6, 8, 10, 15, 18, 19, and 23% for the samples and 14% for the standard. For Toxostat the CVs were 2, 8, 10, 10, 13, and 16%. In general, CVs for VIDAS were slightly larger than the CVs for Toxostat. Day-today variability over 3 days was tested by VIDAS for only six samples (three positive, two negative, and one equivocal) and four standards; CVs ranged from 2 to 15% for the samples and from 6 to 13% for the standards. In conclusion, VIDAS is a rapid, convenient, non-labor-intensive, and easily performed test for the detection of immunoglobulin G antibodies to T. gondii in serum specimens.

Evaluation of the second generation IMx Toxo IgG antibody assay for detection of antibodies toToxoplasma gondii in human sera

“…There have been very few reports in which IMx first or second generation was used (11,12). The method adopted in our study differs in several respects from those described elsewhere (5,(13)(14)(15)(16)(17)(18)(19).…”

“…The 508 serum samples were collected over one month without selection in two hospitals 300 km apart (18,19) and not on the basis of the results obtained with another assay (13) or according to clinical status (5,(14)(15)(16)(17). All the tests were performed in the same laboratory, which avoids variations linked to center (20).…”

Detection of immunoglobulin G (IgG) and IgM antibodies to Toxoplasma gondii: evaluation of four commercial immunoassay systems

“…Laboratory diagnosis relies on detection and quantitation over time of specific Toxoplasma immunoglobulin G (IgG) and IgM antibodies. Detection and measurement of IgG-specific antibodies is rarely problematic, and good sensitivity and specificity have been achieved by a variety of methods (2,5,6,8,11). Detection of IgM antibodies is more problematic because of the reported low degree of test specificity and the clinical implications of a false-positive result, which can lead to unnecessary therapeutic intervention (1,4,7).…”