Evaluation of INNO-LIA syphilis assay as a confirmatory test for syphilis

We evaluated the sensitivity and specificity of a new confirmatory test for treponemal antibodies, INNO-LIA Syphilis (Innogenetics NV, Ghent, Belgium), on a large number of sera from a clinical laboratory. This multiparameter line immunoassay (LIA) uses recombinant and synthetic polypeptide antigens derived from Treponema pallidum proteins. In a single-blinded cross-sectional retrospective study, 289 seronegative sera, 219 seropositive sera, and 23 sera with an indeterminate serological status for syphilis were analyzed. All sera were tested by the T. pallidum hemagglutination assay (TPHA), the immunoglobulin (IgG)-fluorescent T. pallidum absorption assay (IgG-FTA-ABS), and the Venereal Disease Research Laboratory (VDRL) test. In addition, some seropositive samples were analyzed by the 19S-IgM-FTA-ABS test, an enzyme immunoassay (IgM-EIA), and the MarDx immunoblotting assay. Based on a consensus diagnosis derived from conventional serology, all of the sera were classified as positive, negative, or indeterminate, and the results were compared with the findings of the INNO-LIA Syphilis assay. The sensitivity and specificity of the LIA were 100% (219 of 219) and 99.3% (286 of 288), respectively. Compared to TPHA and IgG-FTA-ABS, the new test gave a significantly higher number (P = 0.021 and P < 0.0001, respectively) of correct results than either of the other two tests. The multiparameter INNO-LIA Syphilis assay is a useful confirmatory test for syphilis because it increases the reliability of syphilis diagnosis with respect to current conventional techniques.