Syphilis is a sexually transmitted infection (STI) caused by the bacteria Treponema pallidum. The VDRL test or the venereal disease research laboratory test is a procedure to check if the person has syphilis. The bacteria that causes this STI infection by penetrating into the lining of the mouth or genital area. However, the VDRL test doesn t look these bacteria. Your body makes antibodies in response to antigens that are produced by the cells that the bacteria damages. Antibodies are a type of protein produced by your immune system to fight off invaders like bacteria or toxins. The VDRL test checks for these antibodies in your system, which can let your doctors know whether you have syphilis.