Treponema pallidum Antibodies (FTA-ABS) Serum Test

The FTA-ABS test is a blood test to detect antibodies to the bacteria Treponema pallidum, which causes syphilis. This test is used when a screening test for syphilis is positive to confirm that there is a true infection.

The FTA-ABS becomes reactive 4-6 weeks after infection. Unlike the nontreponemal tests, once the FTA-ABS test becomes reactive, it will remain reactive for many years

FTA antibodies should not be used to follow disease activity or response to treatment since fluorescence has no relation to disease activity. Also, antibody levels will remain elevated for life. False-positive results have been associated with increased or abnormal globulins, antinuclear antibodies, pregnancy, HSV infections, elevated acute-phase reactants, cold agglutinins, Mycoplasma antibodies, age older than 65, and drug addiction. As many as 2% of the general population may be falsely positive. Borderline results are inconclusive results and cannot be interpreted.