Treponema pallidum haemagglutination test for syphilis. Comparison with TPI and FTA-ABS tests.

The Treponema pallidum haemagglutination (TPHA) test, the latest to be developed in the group of specific tests for syphilis, has been described by Tomizawa and Kasamatsu (1966), Rathlev (1967), Tomizawa, Kasamatsu, and Yamaya (1969), and Tringali (1970.) An automated microhaemagglutination technique, the AMHA-Tp test, has been evaluated by Cox, Logan, and Norins (1969) and Logan and Cox (1970). The results of the majority of these authors indicate that the TPHA test, carried out either by a manual or by an automated method, has, in general, a favourable specificity and sensitivity when compared with the Treponemapallidum immobilization (TPI) and fluorescent treponemal antibody absorption (FTAABS) tests in the various stages of syphilis. Of the specific tests for syphilis, the TPI test is limited to a few laboratories because of the expense involved and the highly trained staff required to carry it out. On the other hand the FTA-ABS test can be performed in any laboratory with a suitable fluorescence microscope and staff trained in its use. As with the TPHA test, all the reagents for the FTAABS test are available commercially, but certain problems are involved such as borderline reactions and non-specific reactive test results due to failure of the sorbent to remove all group antibody from a proportion of sera (Kiraily, Jobbagy, and Kovats, 1967). The TPHA test is easier both to perform and to read than either the TPI or the FTA-ABS. These reasons alone make it attractive as a substitute for the more complicated and initially expensive FTA-ABS test in laboratories where it is desired to carry out a simple specific test for syphilis. This study was undertaken to compare the results ofthe TPHA test with those ofthe TPI and FTA-ABS tests on 'problem' sera referred to the laboratory for TPI and FTA-ABS testing. Problem sera are those