Novel Treponema pallidum serologic tests: a paradigm shift in syphilis screening for the 21st century

The mainstay of diagnosis for Treponema pallidum infections is based on nontreponemal and treponemal serologic tests. Many new diagnostic methods for syphilis have been developed, using specific treponemal antigens and novel formats, including rapid point-of-care tests, enzyme immunoassays, and chemiluminescence assays. Although most of these newer tests are not yet cleared for use in the United States by the Food and Drug Administration, their performance and ease of automation have promoted their application for syphilis screening. Both sensitive and specific, new screening tests detect antitreponemal IgM and IgG antibodies by use of wild-type or recombinant T. pallidum antigens. However, these tests cannot distinguish between recent and remote or treated versus untreated infections. In addition, the screening tests require confirmation with nontreponemal tests. This use of treponemal tests for screening and nontreponemal serologic tests as confirmatory tests is a reversal of long-held practice. Clinicians need to understand the science behind these tests to use them properly in syphilis management.