Impact of age, gender, and pregnancy on syphilis screening using the Captia Syphilis-G assay

Abstract

Background: Discordant results have been reported between treponemal-specific enzyme immunoassays (EIA) screening and confirmatory tests such as the Treponemal pallidum particle agglutination (TPPA) assay. The performance of IgG EIA screening in specific populations, such as pregnant women, is not well defined. We reviewed laboratory results of 34,251 samples from individuals who underwent IgG EIA screening at a large Boston academic medical center, so as to calculate positive concordance of these screening tests with a confirmatory TPPA or subsequent rapid plasma reagin (RPR) test by age, gender, pregnancy, and obstetric or gynecologic (Ob/Gyn) service.

Methods: We conducted a retrospective, cross-sectional study of the Captia Syph-G EIA serum samples between 2004 and 2007. Binary regression modeling was used to identify independent associations between demographic variables and positive concordance of EIA screening with RPR and confirmatory TPPA tests.

Results: Of 34,251 samples, 631 (1.8%) had a positive IgG EIA screen. In all, 79% of samples with a positive EIA had a reactive TPPA, and 48% had a positive RPR. Patients less than 40 years of age, females, and women on an Ob/Gyn clinical service had significantly lower rates of positive concordance between EIA screening and TPPA reactivity when covariate adjusted in regression modeling, whereas women on Ob/Gyn service were significantly associated with lower positive concordance with RPR testing.

Conclusions: The relatively low positive concordances between EIA screening and confirmatory studies were more pronounced in low-risk patients, and it is important to define test performance in diverse patient populations.