Syphilis Immunoassay Signal Strength Correlates with Active Infection in Pregnant Women

Abstract

Objective This study aimed to evaluate the association of ARCHITECT chemiluminescent immunoassay (CIA) signal strength (signal-to-cutoff [S/CO] ratio), with maternal syphilis stage, rapid plasma reagin (RPR) reactivity, and congenital syphilis. Study Design A prospective observational study of reverse syphilis screening was conducted. Pregnant women were screened with CIA. Reactive CIA was reflexed to RPR; particle agglutination test (Treponema pallidum particle agglutination [TPPA]) was performed for CIA+/RPR− results. Clinical staging with history and physical was performed, and disease stage was determined. Prior treatment was confirmed. We compared S/CO ratio and neonatal outcomes among the following groups: Group 1: CIA+/RPR+/TPPA+ or CIA+/RPR−/TPPA+ with active syphilis; Group 2: CIA+/RPR−/TPPA+ or CIA+/serofast RPR/TPPA+, previously treated; Group 3: CIA+/RPR−/TPPA+, no history of treatment or active disease; Group 4: CIA+/RPR−/TPPA−, false-positive CIA. Results A total of 144 women delivered with reactive CIA: 38 (26%) in Group 1, 69 (48%) in Group 2, 20 (14%) in Group 3, and 17 (12%) in Group 4. Mean (±standard deviation) S/CO ratio was 18.3 ± 5.4, 12.1 ± 5.3, 9.1 ± 4.6, and 1.9 ± 0.8, respectively (p < 0.001). Neonates with overt congenital syphilis occurred exclusively in Group 1. Conclusion Women with active syphilis based on treatment history, clinical staging, and laboratory indices have higher CIA S/CO ratio and are more likely to deliver neonates with overt evidence of congenital syphilis.

Data on the Relationships of Signal-To-Cutoff Ratios of Elecsys HIV Antigen/Antibody and Elecsys Syphilis Assays to Subsequent Confirmatory Testing at an Academic Medical Center

“…1 (panel A) shows a flow diagram of the syphilis testing in the retrospective study. Multiple studies have shown an association of the signal-to-cutoff (S/CO) value of syphilis immunoassay tests with subsequent positive confirmatory testing indicating either past or current infection [1] , [2] , [3] , [4] . In the reverse algorithm, confirmation testing typically entails RPR as the next test following a positive syphilis antibodies result [5] .…”

Confirmation value of Western blotting in detecting anti-treponema pallidum specific antibodies with suspicious results

“…However, false-negatives can occur with TPPA because of the defects in coating and antigen selection, and the subjective judgment of results [ 5 ]. It has also been reported that a certain percentage of biological false positives can be detected with TPPA [ 5 – 7 ]. In this study, samples with inconsistent results of preliminary screening of anti-TP antibodies by ELISA and retest by TPPA were taken as experiment subjects for other WB tests.…”

Confirmation Value of Western Blotting in Detecting Anti-treponema Pallidum Specific Antibodies With Suspicious Results

“…It has also been reported that a certain percentage of biological false positives can be detected with TPPA (5)(6)(7). In this study, samples with inconsistent results of preliminary screening of anti-TP antibodies by ELISA and retest by TPPA were taken as objects.…”