Comparison of the VDRL slide, TPI, and FTA-ABS tests in experimental syphilis in rabbits.

The first serological test for syphilis, developed by Wassermann, Neisser, and Bruck (1906), was a complement-fixation test for reagin activity. Many tests for reagin activity have been developed since then, including the Kline, Kahn, Hinton, Kolmer, Mazzini, and VDRL slide tests. However, none of these is absolutely specific for syphilis. The VDRL slide test (Harris, Rosenberg, and Riedel, 1946), which utilizes a cardiolipin-lecithin antigen, is that most widely used in the United States. The Treponema pallidum immobilization (TPI) test, developed by Nelson and Mayer (1949), was the first serological procedure utilizingthe causative organism Treponema pallidum as the test antigen. Although several treponemal tests of various sensitivities and specificities have subsequently been developed, the TPI test is, at present, the most widely known verification test for diagnostic problem cases, but it is not easily performed and is available in only a few reference laboratories. The most promising procedure for TPI replacement is the fluorescent treponemal antibodyabsorption (FTA-ABS) test (1965), which incorporates the sensitivity and specificity of immunofluorescence techniques. This test is a modification of the original procedure (Deacon, Falcone, and Harris, 1957), in which a sorbent prepared from the nonpathogenic Reiter treponeme (Stout, Kellogg, Falcone, McGrew, and Lewis, 1967) is used to remove the non-specific immunofluorescence due to several factors, including antibody to the common (group) antigen. The FTA-ABS is a less complicated procedure and is easier to perform than the TPI test. In previous evaluations confined to human patients, the FTA-ABS test compared favourably with other serological methods (Hunter, Deacon, and Meyer, 1964; Deacon, Lucas, and Price, 1966) in sensitivity and specificity in the detection of current or previous syphilitic infections. This paper reports a retrospective study comparing results of FTA-ABS, TPI, and VDRL slide quantitative testing of sera of normal rabbits and those with experimental syphilis or cuniculosis.