FTA-200, FTA-ABS, and TPI Tests in Serodiagnosis of Syphilis

Abstract

IN 1957 Deacon and associates (1) introduced the fluorescent treponemal antibody (FTA) test for the sero,diagnosis of syphilis. The test as originally described was report.ed to have a satisfactory level of sensitivity and specificity (2) and showed promise of becoming a satisfactory substitute for the more complex, expensive, and ge.nera,lly unavailable Treponem'a pa,llidum immobilization (TPI) test. With the introduction of improved reagents, the FTA test apparently became more sensitive but less specific (3). Subsequently, several modifications including the FTA-200 test (3) were described and evaluated. The results of these studies indicated that the FTA tests were relatively specific but generally less, sensitive than the TPI test, that the reactivity could be adjusted by dilution of the test serum (4), and that the Reiter strain of T. pallidum a,ppeared to give comparable results (5). In 1962 Deacon and Hunter (6) reported that the reactions previously encountered were due to group or common treponemal antibodies. Studies indicate,d that the removal of these antibodies by absorption with Reiter treponemes resulted in specific staining of the T. pallidum Nichols strain. Recently Hunter and associates (7) described an FTA-absorption (FTA-ABS) procedure that appears to give results which are both highly sensitive and specific. In this procedure the serum to be tested is first absorbed with a standardized preparation of sonically disrupted Reiter treponemes to remove the group or common treponemal antibody component. After removal of this nonspecific antibody, the serum is tested at a 1: 5 dilution with the FTA technique. Our study was designed to determine the reproducibility, specificity, and sensitivity of the FTA-200 test. Comparative results with the FTA-ABS procedure on a smaller number of cases also are described.