Abstract:

Objective To compare the diagnostic performance of two syphilis reverse testing protocols recommended by the U.S. Centers for Disease Control and Prevention （USCDC） and the European Centre for Disease Prevention and Control （ECDC） within maternal and child populations， and to explore the factors contributing to false-positive results in chemiluminescent immunoassays （CLIA）. Methods A retrospective analysis was performed on serological test results from 109，003 patients collected between 2021 and 2023. All participants were initially screened for specific syphilis antibodies using CLIA， and those with positive results underwent confirmatory testing with both the toluidine red unheated serum test （TRUST） and the Treponema pallidum particle agglutination assay （TPPA）. The kappa statistic was employed to assess the diagnostic agreement between the USCDC and ECDC protocols， while also analyzing the distribution patterns of CLIA false-positive results across varying S/CO value ranges and demographic groups. Results Both protocols achieved a syphilis positivity rate of 0.34%. The hospital's high-prevalence syphilis screening program identified no cases with CLIA-positive or TRUST-positive but TPPA-negative results， suggesting high specificity in this population. The two protocols demonstrated perfect agreement with a Kappa value of 1.0， indicating no significant difference in diagnostic performance between maternal and child populations. CLIA exhibited a true positive rate of 71.04%， which was positively correlated with S/CO values： 21.88% when 1.0 < S/CO ≤ 3.0 and 100% when S/CO > 10. The highest false positive rate for CLIA （38.75%） was observed among young adults， while the largest proportion of false positives-reaching 40.00%—was associated with pregnancy and abortion status. Conclusions The two reverse detection methods for syphilis exhibit comparable diagnostic efficacy in women and children from populations with low syphilis prevalence. CLIA demonstrates high sensitivity； however， when the S/CO ratio is less than 10， particularly in adult women of childbearing age， clinicians should remain vigilant for potential false-positive results to prevent misdiagnosis and unnecessary medical interventions.

Key words: syphilis, reverse detection process, S/CO value, false-positive