Detection of biological false positive syphilis serum reactions.

a lipoidal fraction, which, acting as a hapten, combines with the protein of the treponema and stimulates thl? production of antibodies (reagin) which can be measured by the so-called reagin tests. The first treponemal test using T. pallidum was introduced by Nelson and Mayer' in 1949 when they described the Treponema pallidum immobilisation test (TPI). In this test the serum of patients showing evidence of clinical immunity was able to render immobile living T. pallidum which had been obtained from primary experimental testicular lesions in rabbits. In 1957 Deacon and co-workers' introduced the fluorescein trepo~emal antibody test (FTA) as a substitute for the expensive Treponema pallidum immobilisation test. The new FTA test was very sensitive but gave some false positive results because it detected antibodies in man to the essentially non-pathogenic treponemata. Hunter et al.' absorbed the cross-reacting antibodies from the serum by treatment with Reiter's treponema, which is a cultivable, avirulent strain of Treponema. This new FTA-ABS test is more sensitive and specific for T. pallidum and enables false positive reagin reactions to be detected. We emphasise, however, that although this test is highly specific, this specificity is not absolute. Because of its ease and inexpensiveness, the FTA-ABS test is replacing the TPI test for confirmation of the presence of syphilis when the results of the reagin tests are in question.' It is also widely accepted as the standard by which false positive reactors to reagin tests for syphilis are defined. The specificity of the FTA-ABS test is influenced by the antigenic composition of T. pallidum, sharing antigens with other spirochaetes, and by cross-reacting group antibodies. Information concerning the antigenic structure of T. pallidum is incomplete. Limited studies have shown the Highly specific for diagnostic purposes, but useless for ·control of treatment. Only occasional biological false positive results. our series Not used in Excellent for control of treatment ] Diagnostically useful, but prone to bioI. false positive reactions