Fluorescent Treponemal Antibodies (FTA)
Antibodies in the blood against the bacteria Treponema pallidum, which is responsible for the disease syphilis, can be detected by a fluorescent technique. These fluorescent treponemal antibodies (FTA) are not present in the blood of people who have not had the sexually transmitted disease syphilis (or the rare skin disease yaws which is associated with very poor hygiene).
Antibodies form in blood after infection with T. pallidum, and remain for many years. Thus the test may remain positive for years after successful treatment.