700: Diagnostic accuracy of Abbott ARCHITECT Syphilis TP chemiluminescent immunoassay in pregnant women

Abstract

An alternative to a traditional syphilis diagnostic algorithm, the reverse sequence algorithm (treponemal antibody with reflex to rapid plasma reagin (RPR)) utilizes a screening test such as Abbott ARCHITECT Syphilis TP chemiluminescent immunoassay (CIA) to provide objective, rather than subjective, results. We evaluated the diagnostic accuracy of the CIA screen in pregnant women compared to the traditional RPR prior to clinical implementation of the reverse algorithm at our hospital. Prospectively collected blood samples from routine prenatal RPR tests were collected and frozen. Samples were batch-tested with treponemal-specific CIA (index test). Women with reactive (positive) RPR had particle agglutination assay (TPPA, gold standard) available for analysis; for RPR-/CIA+ samples, TPPA was performed. We calculated sensitivity, specificity, predictive value, and false positive rate of the CIA test in pregnant women and evaluated perinatal outcomes of women with reactive CIA. Of 1,605 specimens, 35(2.1%) were RPR+, including 24(69%) CIA+/TPPA+ and 11(31%) CIA-/TPPA- (false positive RPR) (Figure 1). Of 1,570 RPR- specimens, 14(0.9%) were CIA+, including 13(93%) confirmed TPPA+, and 1(7%) TPPA- (false positive CIA). Diagnostic performance of the CIA (with 95% CI) was: sensitivity 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%)(Table 1). Among 37 CIA+/TPPA+ women, 11(30%) had previously treated syphilis, 19(51%) had active infection, and 7(19%) had RPR- status which did not require treatment or investigation by the local health department. There was no difference in age, parity, or race/ethnicity among women with RPR+/CIA+/TPPA+ versus RPR-/CIA+/TPPA+ results. One stillbirth occurred in a woman with early, active RPR+/CIA+/TPPA+ syphilis identified at delivery; no adverse perinatal outcomes occurred among women with RPR-/CIA+/TPPA+ results. Compared with the traditional RPR screening test, the treponemal-specific CIA accurately diagnoses current or past syphilis in pregnancy. While women with RPR+/CIA+/TPPA+ and RPR-/CIA+/TPPA+ results had similar demographic characteristics, the clinical significance of RPR-nonreactive status in pregnancy is unclear: adverse perinatal outcomes were limited to women with untreated, RPR+/CIA+/TPPA+ results in our study.View Large Image Figure ViewerDownload Hi-res image Download (PPT)