Syphilis Immunoassay Signal Strength Correlates with Active Infection in Pregnant Women

Amanda C. Zofkie, Angela R. Seasely, Vanessa L. Rogers, Donald D. McIntire, Scott W. Roberts, Emily H. Adhikari, Donna Gaffney

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Objective â 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 â 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 â 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 â 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.

Original languageEnglish
Pages (from-to)671-678
Number of pages8
JournalAmerican journal of perinatology
Issue number7
StatePublished - Jun 1 2020


  • ARCHITECT Syphilis TP immunoassay
  • congenital syphilis
  • pregnancy
  • reverse sequence screening algorithm
  • signal strength
  • signal-To-cutoff ratio


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