[The problem of determining Treponema-specific IgM-antibodies with the TPHA test in primary syphilis]

Approximately 10% of the investigated 49 patients with primary syphilis are non-reactive in the TPHA test if the standard technique is used. The reason for this observation can be elucidated by the ELISA technique. Only patients are affected in a second phase of immunological defence which is characterized by identical serum titres of treponemal IgM and IgG antibodies. The rate of TPHA false non-reactive results in primary syphilis can be diminished by using the test with a starting serum dilution of 1:5 instead of 1:20.