Treponema pallidum haemagglutination test for syphilis. Evaluation of a modified micro-method.

Passive haemagglutination of erythrocytes sensitized with antigen is an extremely sensitive method for the detection of antibody. Its application to the serological diagnosis of syphilis was first reported by Rathlev (1965, 1967), using a haemagglutination technique for the detection of specific antitreponemal antibody in which formolized tanned sheep cells sensitized with ultrasonicated material from pathogenic Treponema pallidum (Nichols strain) were used as antigen. This was modified by Tomizawa and Kasamatsu (1966) and Tomizawa, Kasamatsu, and Yamaya (1969), who introduced a different absorbing reagent to remove cross-reacting antibodies. The T. pallidum Haemagglutination Assay (TPHIA) was originally described as a macro-method, reagents for which are available commercially. An automated quantitative micro-haemagglutination assay, the AMHA-Tp test, was developed and evaluated by Cox, Logan, and Norins (1969) and Logan and Cox (1970). Tringali (1970), Cox, Logan, and Stout (1971), Uete, Fukazawa, Ogi, Takeuchi (1971), Le Clair (1971), and Gamer, Backhouse, Daskalopoulos, and Walsh (1972) have also reported on the clinical usefulness of the TPHA test. Its overall specificity and sensitivity are thought to be comparable to those of the FTA-ABS and TPI tests, although the latter has been used in only a minority of the series reported; it is thought to be less sensitive than the FTA-ABS test in primary syphilis. In this study an evaluation of a modified qualitative micro-TPHA technique was undertaken to assess its usefulness as a qualitative screening test for the diagnosis of treponemal infection and its specificity and sensitivity compared with the TPI and FTAABS tests. The technique was a manual method based on the automated micro-haemagglutination test for detection of specific treponemal antibodies described by Cox and others (1969). It was found that economy of serum and reagents, so reducing the cost per test, was possible without loss of sensitivity or specificity.