Four serologic tests for syphilis: results with comparison of selected groups of sera

The specificity of the fluorescent treponemal antibody-absorbed (FTA-Abs) test was assessed for 17 sera from syphilitic patients that were nonreactive in the Treponema pallidum immobilization (TPI) test but reactive in the FTA-Abs test. Thirty-three other sera from syphilitic patients and 19 sera from nonsyphilitic individuals were also examined by fluorescent treponemal and microhemagglutination Treponema pallidum (MHA-TP) tests and by the enzyme-linked immunosorbent assay (ELISA). Specific absorptions of sera with calf thymus DNA or Treponema pallidum biotype Reiter (Reiter treponemes) were performed. In quantitative immunofluorescence assays (IFA) with antihuman IgG and IgM conjugates, results were similar to those for reactive sera from a control group. Results of both the MHA-TP and ELISA tests supported the specificity of the FTA-Abs test; reactivity in the latter was not removed by specific absorption either with calf thymus DNA or with Reiter treponemes. This evaluation suggests a format for serodiagnosis in cases in which test results are discrepant.