Syphilis Specific Treponemal Tests
Specific Treponemal Tests
Because of the decreased specificity of the non treponemal tests, positive RPR and VDRL tests are confirmed with the more precise tests such as the fluorescent treponemal antibody absorption test (FTA-ABS). The FTA-ABS test is also performed in patients with clinical evidence of syphilis for whom the nontreponemal test result is negative. Its main use is to rule out biologic false-positive reagin test reactions and to detect late syphilis in which the reagin test result may be nonreactive. FTA-ABS measures antibody directed against T. pallidum rather than from tissue (reagin), as with the RPR and VDRL tests. False-positive FTA-ABS test results occur most frequently in patients with autoantibodies. A patient who has a reactive treponemal test usually will have a reactive test for a lifetime, regardless of treatment or disease activity. 15% to 25% of patients treated during the primary stage may revert to being serologically nonreactive after 2 to 3 years. Treponemal test antibody titers correlate poorly with disease activity and should not be used to assess response to treatment. The FTA-abs is a standard indirect immunofluorescent antibody test that uses T. pallidum harvested from rabbit testes as the antigen.
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