Syphilis is a venereal disease caused by the spirochaete microorganism Treponema pallidum. As this organism cannot be cultured in vitro the diagnosis of syphilis depends on the correlation of clinical data with the specific antibody demonstrated by serological tests.
Serological screening tests for syphilis utilising cardiolipin and lecithin as antigens are simple to perform but biological false positive (BFP) reactions occur frequently because these tests use non-treponemal antigens1. The TPI and FTA-ABS tests utilise pathogenic T. pallidum as the antigen but these tests present some difficulties for routine serodiagnosis. The TPI test requires living pathogenic T. pallidum and the FTA-ABS test requires a fluorescence microscope. Both tests require a high level of expertise.
TPHA assays have been shown to be a convenient and specific test for the diagnosis of treponemal infection, having a specificity similar to that of the TPI test and a sensitivity comparable to that of the FTA-ABS test. It requires minimal laboratory equipment and is very simple to perform. It can be used in conjunction with automated liquid handling systems for improved throughput in the busy laboratory.