An immunofiltration device for the simultaneous detection of non-treponemal and treponemal antibodies in patients with syphilis

Objective The development of a rapid immunofiltration (flow-through) test for the simultaneous detection of non-treponemal and treponemal antibodies in the serum of patients with syphilis. Methods The assay is rapid, inexpensive, and requires limited expertise in interpreting the results. The test is based on the principle of immunofiltration, with two antigens and control material spotted on the membrane of a through-flow device. A positive test is characterised by the appearance of three red/magenta spots within 2–10 min. Results A total of 376 banked serum samples obtained from the Georgia Public Health Laboratory was examined by the flow-through test, the rapid plasma reagin (RPR) test and the Treponema pallidum passive particle agglutination assay (TPPA). The sensitivity and specificity of the non-treponemal spot were 96.5% and 97.7%, respectively, when compared with the RPR test, and the sensitivity and specificity of the treponemal test spot were 97.3% and 99.1% when compared with the TPPA test. In addition, the test yielded equivalent results to those obtained in comparator tests when 104 sera from cases of syphilis of known stage, 49 sera from diseases other than syphilis and 23 sera known to exhibit biological false-positive reactions were tested in parallel. Conclusions These results indicate that the dual treponemal and non-treponemal assay could be used as a screen and confirmatory test for the serological diagnosis of syphilis in remote or resource-poor settings where there is a need to provide counselling and treatment at the initial consultation.