The Impact of Analytical Sensitivity on Screening Algorithms for Syphilis

To the Editor: Assays for syphilis serology can be broadly divided into 2 categories; treponemal tests that detect antibodies against the infectious agent Treponema pallidum , and nontreponemal tests that measure antibodies against nonspecific antigens, such as cardiolipin. Historically, syphilis diagnosis has used a nontreponemal assay such as rapid plasma reagin (RPR) for screening, followed by a treponemal assay to confirm syphilis infection in screen-positive patients. With the increased availability of automated assays for treponemal antibodies, however, many laboratories have shifted to a “treponemal-first” algorithm for syphilis testing. The merits of the 2 approaches have been debated in the literature in terms of clinical utility and cost-effectiveness (1, 2). The main difference between the 2 approaches is the identification of treponemal-positive,RPR-negative patients when a treponemal-first algorithm is used (3). Discriminating between latent syphilis infection and a false-positive screening test result can be challenging for patients without a clear history of prior disease. In such cases, the CDC has recommended retesting samples with a second treponemal assay to confirm the presence of antitreponemal antibodies (4). For such an algorithm to be valid, the analytical sensitivity of the confirmatory treponemal …