Fluorescent treponemal antibody testing.

Contradictory reports have been published on the value of fluorescent protein tracing as a serological test for syphilis. The authors believe that this is due mainly to differences in technique and especially to variations in the quality of the conjugate used. They describe the preparation of a fluorescein isothiocyanate (FITC) immune serum conjugate, which they characterize by its antihuman-globulin titre, FITC/protein ratio and staining effect. The fluorescent treponemal antibody (FTA-50) test performed with this conjugate gave better agreement with the TPI test than any of four other serological tests with which it was compared. Its sensitivity is also good, being equal to that of the T. pallidum complement-fixation (TPCF) test. Nevertheless, the FTA-50 test is not absolutely specific and, as a screening procedure before TPI testing, a combination of the TPCF test with the cardiolipin complement-fixation test appears to be simpler, more sensitive and cheaper. Further study is needed with a view to the elimination of non-specific staining and standardization of the conjugate and antigen before the FTA-50 test can replace the TPI test.