Which of the following is classified as a treponemal test for syphilis?

The FTA-ABS test, or Fluorescent Treponemal Antibody Absorption test, is classified as a treponemal test for syphilis because it specifically detects antibodies that are produced in response to the Treponema pallidum bacterium, which causes syphilis. Treponemal tests, like the FTA-ABS, are designed to confirm the presence of the infection by identifying these antibodies.

In contrast, RPR (Rapid Plasma Reagin) and VDRL (Venereal Disease Research Laboratory) tests are considered non-treponemal tests. These tests do not detect antibodies specifically against the Treponema pallidum bacterium but rather measure reagin, which is an antibody-like substance that is formed in response to cellular damage caused by the disease. Non-treponemal tests are primarily used for screening, while treponemal tests are used for confirmation due to their specificity.

Therefore, the FTA-ABS test stands out as the correct choice in this context, as it directly assesses the immune response specifically linked to treponemal infections, making it a crucial component in the diagnosis and confirmation of syphilis.