Because of difficulty in culturing Tp, syphilis is suspected based on clinical symptoms, nontreponemal screening tests, and darkfield microscopy. Reactive nontreponemal tests not only support the diagnosis in the presence of early or late syphilis lesions, but also offer a diagnostic clue in latent subclinical syphilis. They are also an effective tool for detecting cases in epidemiologic investigations. The FTA may be used to resolve discrepancies between laboratory results and clinical impressions. A positive VDRL strongly suggests neurosyphilis.
Reactivity appears at the same time as reactivity in nontreponemal tests.
In secondary and latent stages, treponemal tests are positive in virtually all cases. Unlike nontreponemal tests, the FTA-Abs will usually remain reactive despite adequate therapy. This is particularly true for primary and secondary syphilis where the nontreponemal tests usually revert to negative with successful treatment. Inconclusive test reports indicate the initial specimen submitted has been tested twice and cannot be interpreted as either reactive or nonreactive. If it is the second specimen submitted on a patient and the report is again inconclusive, it is impossible to state definitively that the patient does or does not have syphilitic infection.