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The results of serological investigations with the treponemal haemagglutination (TPHA) test are reported in a large number of luetic and non-luetic patients. From these the following conclusions can be drawn: (1) The sensitivity of the TPHA test is decreased if the test is carried out with micromethods; however, in our opinion, the same degree of sensitivity can be obtained either with the macromethod at dilution 1/80-1/60 or with micromethods at 1/20-1/40. (2) The sensitivity of this test is high, being similar to that of the fluorescent treponemal antibody absorption (FTA-ABS) test in primary and secondary syphilis and even higher than that of the FTA-ABS test in treated subjects. (3) The specificity of the reaction is high, as demonstrated by examining sera in patients with a negative history and clinical examination together with negative results to Treponema pallidum immobilisation (TPI) and FTA-ABS tests, and by studying biological false positive sera. (4) For the serological screening, it may be sufficient to perform the TPHA test with the 1/20-1/40 micromethod together with the Venereal Disease Research Laboratory (VDRL) test. In patients with suspected syphilis, it is advisable to perform the TPHA test by the macromethod, in combination with the FTA-ABS test.

The Authors studied the possibility to use, for the carrying out of the TPHA micromethod, higher serum dilutions, as preliminary investigations had pointed out an insufficient sensitivity of the reaction performed at the 1:80 - 1:160 dilutions, particularly in the primary-secondary phase of the luetic infection. The Authors controlled, preliminarily, that at the dilutions studied, no unacceptable increase of spontaneous hemagglutinations and false positive reactions took place in the test sera. The investigation stressed the acceptability of the methodological modification set forth.