A treponemal test is a blood test used to diagnose infections caused by the bacterium Treponema pallidum, which is responsible for syphilis. This test detects antibodies that the body produces in response to the infection. It is often used after a non-treponemal test, which screens for syphilis, to confirm the diagnosis. Treponemal tests are highly specific and can remain positive even after successful treatment of syphilis. Common types of treponemal tests include the FTA-ABS (Fluorescent Treponemal Antibody Absorption) test and the TP-PA (Treponema pallidum Particle Agglutination) test. These tests help healthcare providers determine the presence of a current or past infection.