Which test is most specific for diagnosing syphilis?

The Fluorescent Treponemal Antibody Absorption (FTA-ABS) test is considered the most specific test for diagnosing syphilis. This test detects antibodies that are specifically generated against Treponema pallidum, the bacterium that causes syphilis. Unlike non-treponemal tests, such as the Rapid Plasma Reagin (RPR) or the Venereal Disease Research Laboratory (VDRL) test, the FTA-ABS is not affected by other conditions or diseases, making it a more definitive assay for confirming a syphilis diagnosis.

Non-treponemal tests often yield false positive results due to various factors, such as other infections or inflammatory conditions. Thus, they are typically used for initial screening or as part of a follow-up to assess treatment response rather than for definitive diagnosis. The FTA-ABS, being treponemal, is highly specific for syphilis and is employed to confirm positive results from these initial screenings, ensuring that the diagnosis is accurate and reliable. Therefore, in the context of diagnosing syphilis, FTA-ABS stands out as the most specific test available.