Performance of CAPTIA SelectSyph-G Enzyme-Linked Immunosorbent Assay in Syphilis Testing of a High-Risk Population: Analysis of Discordant Results

Using the Captia Select Syph-G enzyme-linked immunosorbent assay (ELISA), we analyzed the sera of 1,771 patients from a high-risk population attending sexually transmitted disease (STD) clinics. We focused on discrepancies between the results of the immunoglobulin G (IgG) ELISA and theTreponema pallidum hemagglutination (TPHA) test. We identified 57 patients (3.22%) with conflicting results in the IgG ELISA and TPHA test. In order to resolve these discrepancies, these patients’ health records were reviewed and additional serological tests (rapid plasma reagin, IgM ELISA, fluorescent treponemal antibody absorption, and Western blotting) were performed. We subsequently diagnosed 22 of these 57 (38.6%) patients with late latent syphilis. None of the patients with discordant test results was diagnosed with early syphilis. We followed 35 of these 57 patients, analyzing two consecutive serum samples at 3 weeks and at 3 months. Discordant results persisted in 12 (33.3%) patients. We successfully resolved the test result discrepancies for 28 patients (80%) involved in follow-up. Captia SelectSyph-G ELISA showed a sensitivity of 99.0%, a specificity of 98.0%, and positive and negative predictive values of 99.3% and 97.2%, respectively. Based on the results of this study, we conclude that the Captia SelectSyph-G ELISA is a reliable tool for syphilis testing in a high-risk population and recommend the utilization of the Captia SelectSyph-G ELISA as a confirmatory test in at-risk patients.