Fluorescent Treponemal Antibody Absorption
FLUORESCENT TREPONEMAL ANTIBODY ABSORPTION
The fluorescent treponemal antibody absorption (FTA-ABS) test measures a specific antibody made against Treponema pallidum, the bacterium that causes syphilis. The test is reserved for confirmation of a positive screening test for syphilis and distinguishes patients with true infection from those with a false positive result of a screening test. Once a person tests positive, he or she will usually test positive for life. Therefore, the test cannot be used to measure disease activity or differentiate past from present infection.
The FTA-ABS is performed by first heating a patient's serum and mixing it in an extract of nonpathogenic treponemes called "sorbent." This step removes any cross-reacting antibodies that may have developed against treponemes that naturally reside in the human mouth or genital tract. The serum is then layered onto slides containing T. pallidum. Anti-human antibodies labeled with a fluorescent indicator are added, and the slides are examined under a fluorescent microscope. The intensity of fluorescence is quantified using a one (weakly positive) to four (strongly positive) scale. Though very sensitive and highly specific for syphilis, this test tends to be expensive, subjective, and time-consuming, as it requires interpretation by an experienced technician.
JUDITH E. WOLF
Tramont, E. (2000). "Treponema Pallidum." In Principles and Practice of Infectious Diseases, eds. G. Mandell, J. Bennett, and R. Dolin. Philadelphia, PA: Churchill Livingstone.