Which of the following tests is classified as a treponemal assay used to diagnose syphilis?

Explanation

The FTA-ABS (Fluorescent Treponemal Antibody Absorption) test is a treponemal test specifically used to detect antibodies against Treponema pallidum, the causative agent of syphilis. In contrast, the Widal test is for typhoid fever, the Wassermann and Kahn tests are non-treponemal tests, and the VDRL is another non-treponemal test used in syphilis screening.