FIGURE 3: Algorithm with the reverse approach for syphilis diagnosis (starting with treponemal test).

Note: a) Sample must be tested in pure and diluted form to eliminate the possibility of the prozone phenomenon; b) Sample must be diluted in factor 2 and undergo the non-treponemal test again. The results must be provided in titer values (e.g., 2, 4, 8...128) or the last dilution (e.g., 1:2, 1:4, 1:8...1:128) presenting reactivity; c) The detection of treponemal and non-treponemal antibodies suggests active syphilis; d) Treponemal test with a different methodology from the treponemal test already used in the algorithm as the first test. If the third test is not available, the results of each test must be released individually for assessment and clinical conduct;e) Detection of treponemal antibodies only suggests recent syphilis or serological scarring. Assess exposure to risk, signs, symptoms, and history of syphilis treatment for defining clinical conduct; f) Lack of detection of non-treponemal antibodies and non-confirmation of treponemal antibody reactivity suggests no syphilis. Probable false reagent results in the first treponemal test.