Abbott ARCHITECT Syphilis TP Chemiluminescent Immunoassay Accurately Diagnoses Past or Current Syphilis in Pregnancy

Abstract

Objective We evaluate diagnostic accuracy of the ARCHITECT chemiluminescent immunoassay (CIA) screening test in pregnancy, and evaluate pregnancy outcomes among screen-positive women.

Study Design Samples from routine prenatal rapid plasma reagin (RPR) tests were collected between June 22 and August 18, 2017 and frozen. Samples were batch-tested with the Abbott ARCHITECT syphilis TP immunoassay (CIA, index test). We calculated sensitivity, specificity, predictive value, and false positivity. We compared pregnancy and neonatal outcomes among screen-positive women.

Results Of 1,602 specimens, 35 (2.2%) were RPR + ; of those, 24 (69%) were CIA +/Treponema pallidum particle agglutination assay (TPPA)+ and 11 (31%) were CIA-/TPPA-. Of 1,567 RPR- specimens, 14 (0.9%) were CIA + ; of those, 13 (93%) were TPPA + , and one (7%) had a false positive CIA test. Sensitivity of the CIA (95% CI) was 100% (90.5–100%), specificity 99.9% (99.6–100%), positive predictive value 97.4% (86.2–99.9%), and false positive rate 0.06% (0.002–0.4%) for current or past syphilis. Among 37 CIA +/TPPA+ women, seven (19%) had RPR-negative status (Group 1), 11 (30%) had previously treated syphilis (Group 2), and 19 (51%) had active infection (Group 3). One stillbirth occurred in a woman with early, active syphilis identified at delivery; no adverse perinatal outcomes occurred among women in Groups 1 or 2.

Conclusion The ARCHITECT syphilis TP immunoassay accurately diagnoses current or past syphilis in pregnancy. Clinical history and staging remain essential using a reverse algorithm.

Keywords

chemiluminescent - diagnostic accuracy - immunoassay - reverse algorithm - syphilis screening - syphilis in pregnancy - treponemal

Note

This study was presented in poster format at the 39th Annual Society for Maternal-Fetal Medicine meeting held in Las Vegas, Nevada, Feb 11–16, 2019. Abbott Diagnostics provided reagents for the Architect syphilis TP chemiluminescence immunoassay free of charge. Ramani Wonderling and Ollie Hopkins, who were employees of Abbott Diagnostics at the time of the study, provided assistance with the initial sample size calculation free of charge. Internal funding supported the data collection, final statistical analysis, and manuscript preparation for this study.

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