FIGURE 2: Algorithm with the classic approach for syphilis diagnosis (starting with non-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 second test algorithm. When the third test is not available, the results of each test must be released individually for assessment and clinical conduct; e) Detection of treponemal and non-treponemal antibodies suggests active syphilis. Probable false non-reagent results in the first treponemal test; f) Probable false-reaction result for syphilis in the non-treponemal test. Assess other clinical conditions besides syphilis that can generate reaction results in non-treponemal tests.