Comparison Of The Different Syphilis Screening Algorithms In Low Incidence Population

Objective: Serodiagnosis of syphilis has been performed with a traditional or reverse screening algorithm?TSA or RSA?according to considerations of the healthcare provider.Due to the limitations of each algorithm,many healthcare providers and laboratorians have raised the question of which algorithm would be more appropriate for syphilis screening.In the present study,we try to explore the issues related to this controversy.Methods: During the study period,patients were tested with dual algorithms except those from the department of sexually transmitted diseases and obstetrics outpatient submitted for syphilis screening.The TSA in our laboratory initially screened all the sera with a manual toluidine red unheated serum test?TRUST?,refers to a nontreponemal test?NTT?that measures anti-cardiolipin antibodies,and followed by a Treponema pallidum particle agglutination assay?TPPA,a treponemal test,TT?that detect antibodies to TP as a confirmation of reactive screening results.And vice versa,the RSA firstly screened all the sera with an automated chemiluminescence immunoassay(^1stCLIA,Chemclin TP CLIA,Chemclin TP)and reflexively retested with TRUST and confirmed with TPPA for the reactive screening sera.Results: A total of 110663 serum samples were screened.934?0.8%?sera were TRUST-reactive by the TSA.Among the 934 TRUST-reactive results,67?7.2%?were nonreactive by both TPPA and ^1stCLIA?suggesting biologic false-positive,BFP?,840?89.9%?were reactive by both ^1stCLIA and TPPA,and 27?2.9%?were reactive by ^1stCLIA but nonreactive by TPPA.The RSA identified 2259?2.0%?^1stCLIA-reactive results,of which 867?38.4%?were reactive and 1392?61.6%?were nonreactive by TRUST.Among the 867 TRUST-reactive results,840?96.9%?were TPPA-reactive and 27?3.1%?were TPPA-nonreactive,while 1042?74.9%?were reactive and 350?25.1%?were nonreactive by TPPA among the 1392 TRUST-nonreactive results.182 sera from the 350 TPPA-nonreactive sera were further tested by a second CLIA(^2ndCLIA,VITROS Syphilis TPA,VITROS TPA),of which 155?85.2%?were nonreactive and 27?14.8%?were reactive.The 27 ^2ndCLIA-reactive sera were further tested with a treponemal western blot?WB,Euroimmun Ig G Western Blot,Euro WB?assay,of which 11?41%?were indeterminate,6?22%?were nonreactive and 10?37%?were reactive.Among the 10 WB-reactive sera,2 seroconverted to TPPA 1:80+/-after one year later.Conclusions: The RSA identified more patients with reactive serology results;however,it also yielded an increased likely false-reactive rate compared with the TSA.Nevertheless,our further testing results with Euro WB,of which 10?5.5%?were reactive from the 182 CLIA+TRUST-TPPA-sera,and the 2 TPPA 1:80+/-seroconverted sera suggested the likely false-nonreactive TPPA results in identifying the reactive screening treponemal testing results.In conclusion,the ^2ndCLIA test should be implemented for the CLIA+TRUST-TPPA-sera;and the sera should reflexively tested with treponemal WB test for the ^2ndCLIA-reactive serology.If the WB test is not available,the ^2ndCLIA-reactive sera should be retested with follow-ups.