Test Details: Syphilis is a sexually transmitted disease (STD) caused by the bacteria Treponema pallidum. Infection is spread through contact with a syphilic sore, also called a chancre, usually during vaginal, anal, or oral sex. Syphilis can also be spread from a parent to a fetus in pregnancy or to an infant during childbirth. This test look for syphilis antibodies, substances in the blood made by the immune system against the bacteria.