A chemiluminescent test for anti treponemal total antibodies, Liaison Treponema Screen test (LTS), was compared with Treponema Pallidum Particle Agglutination assay (TPPA) against 1022 regular blood donors and 2627 in-and-outpatients attending the laboratories of five hospitals. All positive and doubtful tests were confirmed by Western Blot (WB) and we have discussed the criteria of WB positivity. The results for blood donors were: nonreactive 1022 TPPA and 1021 LTS and doubtful 1 LTS (WB negative) with a concordance of 99.9%.The mean and median index values of the LTS tests (0.175 and 0.15 respectively) were much lower than the doubtful and positive cut-off index values (0.9 and 1.1 respectively).The results for the 2627 patients were: 2423 (92.2%) LTS and TPPA non reactive; 191 (7.3%) LTS and TPPA reactive; 13 (0.5%) LTS and TPPA discordant. Of the 13 patients with discordant tests (1 TPPA reactive vs. LTS nonreactive and 12 LTS reactive or doubtful vs. TPPA nonreactive) 1 was true positive (LTS reactive and TPPA nonreactive), 10 true negative (LTS reactive/doubtful and TPPA nonreactive) and 2 not verifiable. The sensitivity and specificity of LTS were 99.5% and 99.6% respectively; the sensitivity and specificity of TPPA were 99.0% and 100% respectively. In conclusion, LTS and TPPA are similar in sensitivity and specificity, but an automated analyzer as Liaison is more useful than TPPA in laboratories with high workload in syphilis screening.
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