Analysis of Bioplex Syphilis IgG Quantitative Results in Different Patient Populations

Abstract

ᰔBecause of the need to reduce labor costs, many laboratories are replacing the traditional syphilis testing algorithm-screening with a manual nontreponemal test, followed by an antiTreponema pallidum antibody test-with a "reverse" algorithm that uses an automated immunoassay to screen for anti-T. pallidum IgG antibodies. A rapid plasma reagin (RPR) titer determination is then performed on IgG-reactive specimens to (i) verify syphilis by an alternative method and (ii) obtain a titer for patient management. In addition, some laboratories also perform a traditional treponemal assay (fluorescent treponemal antibody absorbed [FTA-ABS] or T. pallidum particle agglutination [TP-PA] assay) on specimens that test positive by an IgG screening assay. A number of studies have shown that anti-T. pallidum IgG immunoassays have sensitivities and specificities that are comparable to those of other treponemal assays and nontreponemal assays (1, 3, 4). As with other highly sensitive screening tests, anti-T. pallidum IgG immunoassays can generate false-positive results, with a lower positive predictive value in low-prevalence populations (2). Yen-Lieberman et al. recently reported that the strength of signal (antibody index [AI]) of the Bioplex 2200 syphilis IgG multiplex flow immunoassay (Bio-Rad Laboratories, Hercules, CA) could be used to identify likely false-positive results and thereby reduce the need for confirmatory testing (5). They demonstrated that specimens with Bioplex AIs of Ն6.0 were always positive when tested with a supplemental enzyme immunoassay (EIA) and therefore proposed an algorithm in which only specimens with a Bioplex syphilis IgG AI of Ͻ6 are subjected to confirmatory EIA. Their study was performed on specimens from a low-prevalence population but did not describe specific population characteristics. In order to further verify the efficacy of the use of the quantitative Bioplex syphilis IgG data, we evaluated AI results from three different patient cohorts (incarcerated individuals, women attending obstetrics and gynecology [OB/Gyn] clinics, and women at delivery) for their ability to predict TP-PA results. Data were stratified by RPR test result. This study was approved by the University of Texas Medical Branch (UTMB) Institutional Review Board.We performed a retrospective review of test results and patient data from the UTMB laboratory information system for serum specimens submitted for routine syphilis testing during December 2010 and January 2011. A total of 1,849, 3,512, and 873 specimens were linked to incarcerated individuals, women attending UTMB clinics for prenatal or gynecological care, and women at delivery, respectively. Among the incarcerated individuals, over 96% of the specimens were from men. The distribution of specimens by individual race or ethnicity was as follows: Hispanic, 49.4%; African-American, 27%; white/non-Hispanic, 21.4%; and other/unknown, 2.2%. Among the OB/Gyn patients, the distribution of specimens by individual race or ethnicity was as follows: Hispanic, 63.1%; white/...

Correlation of Treponemal Immunoassay Signal Strength Values with Reactivity of Confirmatory Treponemal Testing

“…We also found that a BioPlex MBIA signal strength of 7.4 (range, 0 to 8.0) had Ͼ99% correlation with TP-PA reactivity, which supports findings by Loeffelholz et al, who found that a signal strength of 8.0 correlated to Ͼ99% TP-PA reactivity for both low-and high-risk cohorts of patients (5). However, the investigators did note that cutoffs may need to differ when screening low-prevalence versus high-prevalence populations.…”

“…Several analyses have concluded that treponemal immunoassay signal strength values may be used in lieu of confirmatory testing with a second treponemal test: two studies of a microbead immunoassay (MBIA), one of a CIA, and another of an EIA (5)(6)(7)(8).…”

Traditional versus reverse syphilis algorithms: A comparison at a large academic medical center

“…Our retrospective data add to the body of evidence that the screening titer for RPR and quantitative antibody index values for syphilis IgG correlate with the probability of confirmation [4] , [7] , [8] , [23] , [24] . The higher the RPR titer and syphilis IgG value, the more likely a patient is to confirm with subsequent testing.…”

Can a Duplex Non-treponemal and Treponemal Serological Test Help in Improving Syphilis Testing?

“…Some diseases like malaria, hepatitis, viral pneumonia, chicken pox, systemic lupus erythematosus, and others can give false positive result with non-treponemal tests (Ratnam, 2005). Hence, finding obtained with a nontreponemal test needs further confirmation with a treponemal specific test (CDC, 2008 (Loeffelholz et al, 2011 andMishra et al, 2011).…”