Results from the non-conclusive primary and their respective follow-up samples mostly from category #3 and #4 in Table 1.

a Results obtained from the primary samples using the three reference assays, and both the TRF immunoassays (with 10 min and 1 h incubation times), as indicated. All the primary samples are from category #3 and #4, as listed in Table 1. ‘Enzg.’ indicates Enzygnost syphilis EIA. ‘+’, ‘−’ and ‘+/−’ indicate positive, negative and indeterminate results, respectively, as obtained with the mentioned assays.b Results obtained from the thirteen follow-up samples of their respective primary samples using Enzygnost syphilis, TPHA, VDRL and I-L (Inno-Lia Syphilis score line immunoassay) as reference assays, and both the TRF immunoassays (with 10 min and 1 h incubation times), as indicated. Ten out of 13 samples are from category #3 and #4, as listed in Table 1. Each primary sample had either one or none follow-up sample. ‘NA’ indicates that a follow-up sample was not available to us.sample belongs to category #2 as divided in Table 1.Sample not tested with TRF immunoassays in this study.*The antibody titer obtained in TPHA assay is shown in parentheses. ‘ND’, indicates that the test was not done.c Syphilis status indicates whether the person has, or has had syphilis previously, and is based upon the results of previous or follow-up samples and on the available clinical data. ‘N’ indicates a negative and ‘P’ indicates a positive status for syphilis. ‘?’ indicates that true syphilis status is unknown.sample from a new-born baby, with borderline level of maternal antibodies (data not shown).