Which tests are used for diagnosing syphilis?

• A. Nontreponemal tests (VDRL, RPR) only
• B. Treponemal tests (FTA-ABS) only
• C. Nontreponemal tests (VDRL, RPR) and treponemal tests (FTA-ABS)
• D. No reliable tests

Answer: (C)

Diagnosing syphilis relies on two complementary serologic approaches: nontreponemal tests and treponemal tests. Nontreponemal tests such as VDRL and RPR detect antibodies to cardiolipin and are useful for initial screening and for measuring disease activity through titers, which helps monitor response to therapy. However, they can yield false positives in other conditions and may become nonreactive after treatment or be negative in very early infection. Treponemal tests like FTA-ABS detect antibodies directed against Treponema pallidum and are highly specific, remaining reactive for life after infection, which makes them ideal for confirming exposure. But because they stay positive even after successful treatment, they cannot by themselves distinguish active infection from a past, treated one. By using a nontreponemal test for screening (and monitoring) and a treponemal test for confirmation, clinicians achieve the most accurate diagnosis. Therefore, both types of tests are used.