Comparative evaluation of 15 serological assays for the detection of syphilis infection

Retrospective comparison of false-positive result frequencies of 3 syphilis serology screening tests in pregnant and nonpregnant patients at an academic medical center in Appalachia

OBJECTIVE

This study retrospectively compared false-positive result frequencies of 3 syphilis serology screening tests and assessed whether false positivity was associated with pregnancy and age.

METHODS

Results for 3 screening tests were retrieved from the laboratory database, including rapid plasma reagin (RPR) assay between October 2016 and September 2019, BioPlex 2200 Syphilis Total immunoassay between May 2020 and January 2022, and Alinity i Syphilis TP assay between February 2022 and April 2023. The false-positive result frequencies were calculated based on testing algorithm criteria.

RESULTS

False-positive result frequency for BioPlex was 0.61% (90/14,707), significantly higher than 0.29% (50/17,447) for RPR and 0.38% (55/14,631) for Alinity (both P < .01). Patients with false-positive results were significantly older than patients with nonreactive results for RPR (median age: 36 vs 28, P < .001), but not for BioPlex or Alinity. For all 3 tests, the positive predictive values in pregnant women were lower than those in nonpregnant women or men. However, pregnant women did not exhibit a higher false-positive result frequency.

CONCLUSION

Although false-positive result frequencies were low overall for all 3 syphilis serology tests, there is a significant difference between different tests. Pregnancy was not associated with more false-positive results for all 3 tests.

Evaluating the diagnostic accuracy of TpN17 and TmpA recombinant proteins in syphilis detection: a phase II study

Syphilis is a sexually transmitted infection (STI) caused by the spiral bacterium Treponema pallidum. Diagnosis is based on epidemiology, clinical and serology, but serodiagnosis is challenging because distinct clinical forms of the infection may influence serological performance. Several recombinant Treponema pallidum-proteins have already been tested for syphilis diagnosis and they are critical to achieve high accuracy in serological testing. A total of 647 samples were included in the study: 180 T. pallidum-positive samples, 191 T. pallidum-negative samples and 276 sera from individuals infected with unrelated diseases. The diagnostic potential was validated by analysis of ROC curves. For the indirect ELISA, TpN17 (100%) and TmpA (99%) showed excellent AUC values. Sensitivity values were 97.2% for TpN17 and 90.6% for TmpA, while specificity was 100% for both molecules. According to the clinical phase, TmpA ranged from 84% to 97%, with the highest value for secondary syphilis. TpN17 was 100% sensitive for the primary and secondary stages and 93.2% for recent latent syphilis. All clinical phases achieved 100% specificity. Accuracy values showed that TmpA (> 95%) and TpN17 (> 98%) presented high diagnostic accuracy for all clinical stages of syphilis. Cross-reactivity was only observed in one sample positive for Chagas disease (1.5%), when TpN17 was evaluated. On the other hand, TmpA showed reactivity for two samples positive for Chagas disease (3.1%), one sample positive for HBV (1.25%), two samples positive for HIV (9.5%) and one sample positive for HTLV (1.6%). The TmpA antigen's performance was evaluated in multiple studies for syphilis diagnosis, corroborating our findings. However, TpN17 sensitivity values have ranged in other studies. According to clinical stages of the infection, our findings obtained close performance values.

CDC Laboratory Recommendations for Syphilis Testing, United States, 2024

This report provides new CDC recommendations for tests that can support a diagnosis of syphilis, including serologic testing and methods for the identification of the causative agent Treponema pallidum. These comprehensive recommendations are the first published by CDC on laboratory testing for syphilis, which has traditionally been based on serologic algorithms to detect a humoral immune response to T. pallidum. These tests can be divided into nontreponemal and treponemal tests depending on whether they detect antibodies that are broadly reactive to lipoidal antigens shared by both host and T. pallidum or antibodies specific to T. pallidum, respectively. Both types of tests must be used in conjunction to help distinguish between an untreated infection or a past infection that has been successfully treated. Newer serologic tests allow for laboratory automation but must be used in an algorithm, which also can involve older manual serologic tests. Direct detection of T. pallidum continues to evolve from microscopic examination of material from lesions for visualization of T. pallidum to molecular detection of the organism. Limited point-of-care tests for syphilis are available in the United States; increased availability of point-of-care tests that are sensitive and specific could facilitate expansion of screening programs and reduce the time from test result to treatment. These recommendations are intended for use by clinical laboratory directors, laboratory staff, clinicians, and disease control personnel who must choose among the multiple available testing methods, establish standard operating procedures for collecting and processing specimens, interpret test results for laboratory reporting, and counsel and treat patients. Future revisions to these recommendations will be based on new research or technologic advancements for syphilis clinical laboratory science.

Sensitivity and Specificity of Treponemal-specific Tests for the Diagnosis of Syphilis

We conducted a systematic review of relevant syphilis diagnostic literature to address the question, “What is the sensitivity and specificity of the treponemal tests currently approved by the Food and Drug Administration (FDA) for the diagnosis of syphilis (by stage)?” There were 16 treponemal assays evaluated: 13 immunoassays and 3 manual assays (fluorescent treponemal antibody absorbed test [FTA-ABS], microhemagglutination assay for Treponema pallidum antibodies [MHA-TP], Treponema pallidum particle agglutination assay [TP-PA]). MHA-TP and FTA-ABS were less sensitive in primary and secondary syphilis than TP-PA; TP-PA is the most specific manual treponemal assay. There is insufficient evidence to recommend one particular treponemal immunoassay (eg, enzyme immunoassays, chemiluminescence immunoassays, microbead immunoassays) over another based on published performance data. For diagnosis of neurosyphilis, cerebrospinal fluid (CSF) TP-PA has similar performance to CSF FTA-ABS in studies with patients with definitive or presumptive neurosyphilis. However, CSF treponemal testing has limitations in its sensitivity and specificity and should be interpreted within the context of the clinical scenario, additional CSF test results and syphilis prevalence.

2020 European guideline on the management of syphilis

The 2020 edition of the European guideline on the management of syphilis is an update of the 2014 edition. Main modifications and updates include: -The ongoing epidemics of early syphilis in Europe, particularly in men who have sex with men (MSM) -The development of dual treponemal and non-treponemal point-of-care (POC) tests -The progress in non-treponemal test (NTT) automatization -The regular episodic shortage of benzathine penicillin G (BPG) in some European countries -The exclusion of azithromycin as an alternative treatment at any stage of syphilis -The pre-exposure or immediate post-exposure prophylaxis with doxycycline in populations at high risk of acquiring syphilis.

Evaluation of the Elecsys Syphilis electrochemiluminescence immunoassay as a first-line screening test in the reverse algorithms for syphilis serodiagnosis

OBJECTIVES

With the development of the automated treponemal test, new syphilis serodiagnosis algorithms, reverse algorithm, and European Centre for Disease Prevention and Control (ECDC) algorithm have been recommended recently. We investigated the efficacy of an electrochemiluminescence immunoassay (ECLIA) as an initial screening test in the reverse and ECDC algorithms.

METHODS

Samples from 4,771 subjects were included in this study. We performed rapid plasma reagin (RPR), ECLIA, and Treponema pallidum particle agglutination (TPPA) according to these three algorithms. The fluorescent treponemal antibody absorbed (FTA-ABS) test was additionally applied for discordant cases between the RPR and ECLIA results. The FTA-ABS results and the consensus of three algorithms were considered a gold standard.

RESULTS

A total of 208 subjects were diagnosed with syphilis. The traditional algorithm had a sensitivity of 25.96%, specificity of 100%, and accuracy of 96.77%. Both the reverse and ECDC algorithms showed the same diagnostic performance, sensitivity of 95.19%, specificity of 99.96%, and accuracy of 99.75%. The agreements between the traditional algorithm and the other algorithms were 96.9% with a kappa value of 0.415.

CONCLUSIONS

The diagnostic accuracy of the reverse and ECDC algorithms using the ECLIA as a first-line screening test was superior to that of the traditional algorithm.

Comparison of three syphilis algorithms in West China

OBJECTIVE

The study was designed to analyze three different algorithms with the implementation of treponemal tests for detecting suspected syphilis in west China where no syphilis algorithms guideline exists.

METHODS

We retrospectively collected data to reanalyze three syphilis testing algorithms: the classical reverse algorithm, and two options of syphilis screening in European syphilis guideline. The kappa (κ) coefficients were used to compare the concordance between algorithms using different syphilis assays during two periods. A receiver operating characteristic curve was used to determine the optimal S/CO ratios of InTec EIA or Lumipulse® G TP-N assay (CLIA) to predict confirmatory TPPA results.

RESULTS

The agreements between the reverse algorithm and the EU option 1 algorithms were perfect irrespective of EIA or CLIA used (all κ > 0.9). But the agreements between the EU option 2 algorithms and reverse or EU option 1 were not good (κ < 0.4). >50% cases confirmed syphilis infections by reverse or EU option 1 algorithm were missed by EU option 2. There is no very need for a confirmatory TPPA assay in EU Option 1 when S/CO is above 6.12 for CLIA (3.67 for EIA). The false-positive rate was 0.26% above this cutoff level.

CONCLUSIONS

EU Option 1, involving a reactive TT, followed by another TT of a different type and a quantitative NTT if second TT is positive, which is the same as the 2015 UK syphilis algorithm, is recommended. We also propose that when S/CO of the CLIA or EIA is high enough, TPPA confirmation can be omitted from the testing algorithm, and costs would be significantly reduced.

Evaluation of new algorithm using TPLA as an initial syphilis screening test

We retrospectively compared the performance of an existing syphilis diagnostic algorithm with a new algorithm that analyzes the results of Treponema pallidum latex agglutination (TPLA) tests. Of the 100 clinical blood samples, 51 were classified as positive through both Mediace TPLA and ESPLINE TP; 2/51 were classified as negative by Architect Syphilis TP, whereas 1/51 was negative as per LUMIPULSE Presto TP. The false positive rate when the results of Mediace TPLA and ESPLINE TP were combined was 1.96% versus 0% for both Architect Syphilis TP and LUMIPULSE Presto TP. The sensitivity of Mediace TPLA (98%) was comparable to that of Architect Syphilis TP (98%) but lower than that of LUMIPULSE Presto TP (100%). The specificity of Mediace TPLA was 98.0% versus 100% for Architect Syphilis TP, and versus 100% for LUMIPULSE Presto TP. We conclude that the performance of Mediace TPLA in combination with a reverse algorithm is nearly equal to that of enzyme immunoassay (EIA) or chemiluminescence immunoassay (CIA). Because TPLA is low cost, highly sensitive method for IgM detection, and is easy to operate, we have recommended its adoption for initial syphilis screening tests.

Use of Treponemal Screening Assay Strength of Signal to Avoid Unnecessary Confirmatory Testing

BACKGROUND

Our reverse syphilis testing algorithm consists of a treponemal IgG multiplex flow immunoassay (MFI) followed by both rapid plasma reagin titer and the Treponema pallidum particle agglutination (TPPA) test on specimens with a reactive MFI result. We report here the impact of a modified reverse algorithm, in which the strength of signal of the MFI is used to avoid unnecessary TPPA testing.

METHODS

The Bioplex syphilis IgG MFI was used as the syphilis screening assay, and specimens with equivocal (antibody index 0.9 or 1.0), or reactive (antibody index ≥ 1.1) results were further tested by rapid plasma reagin titer and TPPA test. We performed a retrospective, descriptive analysis of all specimens received for syphilis screening between January and May of 2014. A cost analysis was performed, taking into account labor and reagent expenses.

RESULTS

In our diverse patient population consisting of high-risk incarcerated persons, low-risk obstetrical/gynecological patients and high-risk miscellaneous clinic and inpatients, 430 (65%) of 665 MFI-positive specimens had antibody indices of 8 or greater. Greater than 99% of these specimens were reactive by the TPPA test. Avoiding TPPA testing of specimens with an MFI antibody index ≥8 would save over US $4800 annually in laboratory costs.

CONCLUSIONS

The TPPA testing is unnecessary on specimens with MFI antibody indices ≥8. This would substantially reduce the TPPA testing volume and also reduce laboratory expenses.

Comparative evaluation of enzyme-linked immunosorbent assay with rapid plasma reagin for screening of syphilis in blood donors

World Health Organization (WHO) recommends screening of syphilis in low prevalence populations of blood donors by treponemal tests like enzyme-linked immunosorbent assay (ELISA), whereas in India screening is done by rapid plasma reagin (RPR). The present pilot study evaluated the performance of ELISA compared to RPR, keeping Treponema pallidum hemagglutination assay as a reference test. ELISA was equally sensitive (100%), more specific (56.3% vs. 0%), more accurate (83.7% vs. 62.7%), had better positive predictive value (79.4% vs. 62.8%) and negative predictive value (100% vs. 0%), and less biological false positivity (37.2% vs. 20.6%) when compared to RPR. The WHO recommendations of screening for syphilis in low prevalence population of blood donors using ELISA may be adopted for usage in transfusion services that have the facility of ELISA.

False-negative syphilis treponemal enzyme immunoassay results in an HIV-infected case-patient

We present a case report of a false-negative syphilis treponemal enzyme immunoassay test result in an HIV-infected male. While treponemal tests are widely considered to be more sensitive and specific than non-treponemal tests, our findings point to potential challenges using the reverse sequence syphilis screening algorithm.

Prevalence of Traditional and Reverse-Algorithm Syphilis Screening in Laboratory Practice: A Survey of Participants in the College of American Pathologists Syphilis Serology Proficiency Testing Program

CONTEXT

-Syphilis serology screening in laboratory practice is evolving. Traditionally, the syphilis screening algorithm begins with a nontreponemal immunoassay, which is manually performed by a laboratory technologist. In contrast, the reverse algorithm begins with a treponemal immunoassay, which can be automated. The Centers for Disease Control and Prevention has recognized both approaches, but little is known about the current state of laboratory practice, which could impact test utilization and interpretation.

OBJECTIVE

-To assess the current state of laboratory practice for syphilis serologic screening.

DESIGN

-In August 2015, a voluntary questionnaire was sent to the 2360 laboratories that subscribe to the College of American Pathologists syphilis serology proficiency survey.

RESULTS

-Of the laboratories surveyed, 98% (2316 of 2360) returned the questionnaire, and about 83% (1911 of 2316) responded to at least some questions. Twenty-eight percent (378 of 1364) reported revision of their syphilis screening algorithm within the past 2 years, and 9% (170 of 1905) of laboratories anticipated changing their screening algorithm in the coming year. Sixty-three percent (1205 of 1911) reported using the traditional algorithm, 16% (304 of 1911) reported using the reverse algorithm, and 2.5% (47 of 1911) reported using both algorithms, whereas 9% (169 of 1911) reported not performing a reflex confirmation test. Of those performing the reverse algorithm, 74% (282 of 380) implemented a new testing platform when introducing the new algorithm.

CONCLUSION

-The majority of laboratories still perform the traditional algorithm, but a significant minority have implemented the reverse-screening algorithm. Although the nontreponemal immunologic response typically wanes after cure and becomes undetectable, treponemal immunoassays typically remain positive for life, and it is important for laboratorians and clinicians to consider these assay differences when implementing, using, and interpreting serologic syphilis screening algorithms.

Efforts in blood safety: Integrated approach for serological diagnosis of syphilis

Recent efforts in transfusion medicine are focused on improving blood safety as well as establishing effective and efficient diagnostic algorithms for donor screening. To date, syphilis is a transfusion-transmitted infection re-emerged in many countries as a public health threat especially among populations at specific risk. This task requires new diagnostic tools and hemovigilance programs. The current diagnostic methodologies are debated, since presenting limitations and unresolved issues with special regard to the clinical interpretation of serological patterns, especially in asymptomatic patients and in blood donors. Furthermore, the switch from the traditional to alternative diagnostic algorithms underlines the lack of a gold standard, which has not been supported by shared guidelines. Besides, a lot of ongoing clinical trials on the performance of diagnostic assays, on the serological response associated with different pharmacological treatments, as well as on the prevention programs are currently under investigation. Here, we review the recent literature about the diagnosis of syphilis especially for low-risk populations proposing the adoption of an algorithm for blood donor screening that should satisfy the need of increasing safety for transfusion-transmitted infections in the modern blood transfusion centers.

Painful and multiple anogenital lesions are common in men with Treponema pallidum PCR-positive primary syphilis without herpes simplex virus coinfection: a cross-sectional clinic-based study

BACKGROUND

Chancres, the hallmark of primary syphilis, are classically described as single, painless ulcers at the site of Treponema pallidum inoculation. We aimed to determine the frequency of painful or multiple anogenital lesions of primary syphilis among men, whether there was concurrent herpes simplex virus (HSV) infection and whether HIV status altered clinical presentations.

METHODS

This study was conducted among men with T. pallidum PCR-positive lesions, attending a clinic in Melbourne, Australia, between 2009 and 2014. Lesions were also tested with HSV PCR, and syphilis serology undertaken.

RESULTS

183 men with T. pallidum PCR-positive primary anogenital lesions were included. 89% were men who have sex with men, and 10.9% were heterosexual. 38 men (20.8%) were HIV positive. Anal lesions were more common in HIV-positive men (34.2%) than in HIV-negative men (11.6%). Primary lesions were frequently painful (49.2%) or multiple (37.7%), and infrequently associated with HSV (2.7%). Of 37 men with both painful and multiple primary lesions, only 8% had concurrent HSV. Presentation was not significantly altered by HIV status.

CONCLUSIONS

Primary syphilis lesions are often painful and/or multiple in the absence of herpes coinfection, and may be clinically misdiagnosed.

Development of a novel protein biochip enabling validation of immunological assays and detection of serum IgG and IgM antibodies against Treponema pallidum pathogens in the patients with syphilis

In this study, we developed a novel protein biochip methodology that was characterized by dithiobis (succinimidyl undecanoate) (DSU) and specialized for detection of serum IgG and IgM antibodies against Treponema pallidum pathogens in the patients with syphilis, respectively. The biochips were validated by a dimension of atomic force microscope (AFM). The visualized detection limit of IgG antibody on the biochip was 0.39μg/ml. Finally, 286 serum samples from the patients with syphilis were simultaneously tested on the rTpN15-17-47 coated biochips. The results were evaluated in comparison with the assays of T. pallidum particle agglutination (TPPA) and the toluidine red unheated serum test (TRUST). The result demonstrated that the relative positive rate in the 286 patients by biochip was 99.0%, similar to that by TPPA (97.9%, P>0.05) and higher than that by TRUST, (76.2%, P<0.01). The detection specificities were 100% for the biochip and the TPPA and 97.0% for the TRUST. Thus, the protein biochip would provide a useful platform not only for enabling concurrent detection of the infectious antibodies directed against T. pallidum on a larger scale, but also for monitoring therapy modality of the disease.

Evaluation of different confirmatory algorithms using seven treponemal tests on Architect Syphilis TP-positive/RPR-negative sera

The Architect Syphilis TP is considered to be a suitable screening test due to its high sensitivity and full automation. According to the International Union against Sexually Transmitted Infections (IUSTI) 2014 guidelines, however, positive screening tests need confirmation with Treponema pallidum particle agglutination (TP.PA). Among Architect-positive results, samples with a negative non-treponemal test present the major diagnostic challenge. In this multicenter study, we investigated if other, preferable less labor-intensive treponemal tests could replace TP.PA. A total of 178 rapid plasma reagin (RPR)-negative sera with an Architect value between 1 and 15 S/CO were prospectively selected in three centers. These sera were analyzed with TP.PA and six alternative treponemal tests: three immunoblots and three tests on random-access analyzers. The diagnostic performance of the treponemal tests differed substantially, with the overall agreement between the six alternative tests ranging from 44.6 to 82.0%. Based on TP.PA as the gold standard, the INNO-LIA IgG blot, the BioPlex 2200 IgG, and the Syphilis TPA showed a high sensitivity, while the EUROLINE-WB IgG blot, recomLine Treponema IgG blot, and the Chorus Syphilis screen showed a high specificity. However, an Architect cut-off of 5.6 S/CO can serve as an alternative for these confirmatory treponemal tests in case of an RPR-negative result. Treponemal tests show poor agreement in this challenging group of Architect-positive/RPR-negative sera. The most optimal algorithm is obtained by assigning sera with an Architect value >5.6 S/CO as true-positives and sera with a value between 1 and 5.6 S/CO as undetermined, requiring further testing with TP.PA.

Evaluation of the HISCL Anti-Treponema pallidum Assay as a Screening Test for Syphilis

The resurgence of syphilis in recent years has become a serious threat to public health worldwide, and the serological detection of specific antibodies against Treponema pallidum remains the most reliable method for laboratory diagnosis of syphilis. This study examined the performance of the recently launched HISCL anti-Treponema pallidum (anti-TP) assay as a screening test for syphilis in a high-volume laboratory. The HISCL anti-TP assay was tested in 300 preselected syphilis-positive samples, 704 fresh syphilis-negative samples, 48 preselected potentially interfering samples, and 30 "borderline" samples and was compared head to head with the commercially available Lumipulse G TP-N. In this study, the HISCL anti-TP assay was in perfect agreement with the applied testing algorithms with an overall agreement of 100%, comparable to that of Lumipulse G TP-N (99.63%). The sensitivity and specificity of the HISCL anti-TP assay were 100% (95% confidence interval [CI], 98.42% to 100%) and 100% (95% CI, 99.37% to 100%), respectively. Considering the excellent ease of use and automation, high throughput, and its favorable sensitivity and specificity, the HISCL anti-TP assay may represent a new choice for syphilis screening in high-volume laboratories.

Performance Evaluation of CLIA for Treponema Pallidum Specific Antibodies Detection in Comparison with ELISA

OBJECTIVES

In this study we aimed to evaluate the performance effects of chemiluminescence assay (CLIA) for Treponema pallidum specific antibodies detection, and to compare T. pallidum specific antibodies detection accuracy between CLIA and ELISA with TPPA (T. pallidum particle agglutination assay) as a confirmatory test.

METHODS

A total of 865 samples from suspected syphilis patients and preoperative patients were included, in which T. pallidum specific antibodies were simultaneously detected by CLIA and ELISA. Among them, 457 samples were determined by TPPA.

RESULTS

All coefficients of variation (CVs) of ELISA in high-, median-, and low-level samples were more than 5% and the maximum CV was 54.39% in the low-level sample. CVs of CLIA in different-level samples were all below 5%. Among the three assays the Spearman correlation and Kappa coefficients were 0.771 (P ≤ 0.001) and 0.854 (P ≤ 0.001, CLIA vs. ELISA), 0.806 (P ≤ 0.001) and 0.897 (P ≤ 0.001, ELISA vs. TPPA), 0.937 (P ≤ 0.001) and 0.967 (P ≤ 0.001, CLIA vs. TPPA), respectively. The area under the receiver operating characteristic curve (AUC) of CLIA was higher than that of ELISA (0.994 vs. 0.989) with TPPA as the confirmatory test. In 18 discrepant samples the consistency rate between CLIA and TPPA was elevated compared with that between ELISA and TPPA (72.22% vs. 27.78%, P = 0.008). In gray zone, the consistency rate of CLIA with TPPA was higher than that of ELISA with TPPA (90.91% vs. 41.67%, P = 0.027).

CONCLUSIONS

Compared with ELISA, CLIA is more reliable, sensitive and accurate to detect serum T. pallidum specific antibodies. In the future it may be an alternative test with higher sensitivity to ELISA.

Recent trends in the serologic diagnosis of syphilis

Complexities in the diagnosis of syphilis continue to challenge clinicians. While direct tests (e.g., microscopy or PCR) are helpful in early syphilis, the mainstay of diagnosis remains serologic tests. The traditional algorithm using a nontreponemal test (NTT) followed by a treponemal test (TT) remains the standard in many parts of the world. More recently, the ability to automate the TT has led to the increasingly widespread use of reverse algorithms using treponemal enzyme immunoassays (EIAs). Rapid, point-of-care TTs are in widespread use in developing countries because of low cost, ease of use, and reasonable performance. However, none of the current diagnostic algorithms are able to distinguish current from previously treated infections. In addition, the reversal of traditional syphilis algorithms has led to uncertainty in the clinical management of patients. The interpretation of syphilis tests is further complicated by the lack of a reliable gold standard for syphilis diagnostics, and the newer tests can result in false-positive reactions similar to those seen with older tests. Little progress has been made in the area of serologic diagnostics for congenital syphilis, which requires assessment of maternal treatment and serologic response as well as clinical and laboratory investigation of the neonate for appropriate management. The diagnosis of neurosyphilis continues to require the collection of cerebrospinal fluid for a combination of NTT and TT, and, while newer treponemal EIAs look promising, more studies are needed to confirm their utility. This article reviews current tests and discusses current controversies in syphilis diagnosis, with a focus on serologic tests.

Serologic Testing for Syphilis: Benefits and Challenges of a Reverse Algorithm

Syphilis is a human infection of global importance. Its diagnosis can be challenging, requiring construction of a serologic profile based on the results of at least two types of antibody tests: treponemal and nontreponemal. The traditional approach to the serodiagnosis of syphilis has been the use of a nontreponemal screening assay followed by the performance of a treponemal confirmatory test if the initial nontreponemal screening test was reactive. With the increasing availability of automated, easier-to-perform, and rapid treponemal assays, an increasing number of laboratory testing sites are adopting reverse sequence screening for the serodiagnosis of syphilis: screening with a treponemal assay first, then confirmation with a nontreponemal assay and, when necessary, discrepant resolution using another treponemal test. In addition to offering automation and increased throughput, a reverse algorithm can increase disease detection, especially in late latent and early primary stages of infection when the nontreponemal antibody test may be nonreactive. However, a disadvantage to this approach is that there can be an increase in false-positive test results. This article reviews the clinical and workflow benefits and limitations of a reverse testing algorithm and discusses current guidance available from the Centers for Disease Control and Prevention.

Syphilis detection using the Siemens ADVIA Centaur Syphilis treponemal assay

BACKGROUND

Treponemal tests for detecting syphilis should be sufficiently sensitive and specific, especially when used as the first-line method in reverse-algorithm testing. We compared the Siemens ADVIA Centaur® Syphilis assay to 2 other commercial assays in use by the Star-MDC laboratory to evaluate its performance and usability.

METHODS

Agreement between the Siemens ADVIA Centaur Syphilis assay, Siemens IMMULITE® 2000 Syphilis Screen, and Biokit bioelisa Syphilis 3.0 assay was evaluated using 1251 patient samples (50 from known positives, 701 from patients referred for syphilis testing, and 500 from pregnant women). Reactive samples (i.e., reactive according to at least two of the three treponemal methods) were further evaluated using Western blot IgG and IgM, and Venereal Disease Research Laboratory (VDRL) testing.

RESULTS

Overall, positive and negative agreement was 100% between the Centaur and IMMULITE assays. In this study, overall agreement was 99.92% between either of the Siemens assays and the Biokit assay; positive agreement was 99%, and negative agreement was 100%. Overall, 0.88% (11/1251) of the samples were interpreted as positive/reactive based on the combined positive results by the ADVIA Centaur, IMMULITE 2000, and bioelisa assays; a positive Euroline anti-Treponema pallidum IgM blot; and a VDRL result of ≥1:8. In this study, no false-reactive samples were identified using this method.

CONCLUSION

The Centaur Syphilis assay performance is comparable to the other 2 commercial assays.

Characterization of sera with discordant results from reverse sequence screening for syphilis

Reverse sequence screening for syphilis (RSSS) (screening with treponemal tests, followed by confirmation with nontreponemal tests) has been increasingly adopted. CDC recommends confirmation of discordant results (reactive EIA/CIA and nonreactive nontreponemal test) with Treponema pallidum particle agglutination assay (TP-PA). We characterized sera with discordant results from RSSS with Architect Syphilis TP CIA. Among 15,713 screening tests using Architect Syphilis TP at Seoul National University Gangnam Center between October 2010 and May 2011, 260 (1.7%) showed reactive results. Rapid plasma reagin (RPR) and TP-PA were performed on 153 available sera among them. On sera with discordant results between Architect Syphilis TP and TP-PA, INNO-LIA Syphilis Score and FTA-ABS were performed. Among 153 sera, RPR was nonreactive in 126 (82.4%). Among them, TP-PA was positive in 103 (81.7%), indeterminate (±) in 7 (5.6%), and negative in 16 (12.7%). Out of 16 CIA(+)/RPR(-)/TP-PA(-) sera, INNO-LIA Syphilis Score and/or FTA-ABS were negative on 14 sera. Out of 7 CIA(+)/RPR(-)/TP-PA(±) sera, INNO-LIA Syphilis Score and FTA-ABS were positive/reactive in 6 sera. RSSS with confirmation by TP-PA on sera with discordant results between Architect Syphilis TP and RPR effectively delineated those discordant results and could be successfully adopted for routine checkup for syphilis.

Which algorithm should be used to screen for syphilis?

PURPOSE OF REVIEW

A growing number of laboratories have implemented a reverse screening algorithm for syphilis testing, which has created confusion among many healthcare providers. This review focuses on recent data addressing the clinical and economical impact of reverse screening and discusses the advantages and limitations of the traditional and contemporary algorithms.

RECENT FINDINGS

Screening for syphilis using a treponemal assay detects a higher number of patients with reactive results compared to traditional screening by rapid plasma reagin (RPR). Furthermore, a significant percentage of patients who are reactive by a treponemal screening assay are nonreactive by RPR. These discordant results may occur in patients with past, treated or untreated syphilis; early syphilis; or no syphilis. Recent reports suggest that the reverse screening algorithm may result in increased patient follow-ups, overtreatment, and potentially higher cost. However, other data suggest that reverse screening facilitates the detection of latent and early syphilis, while offering an objective and automated screening approach.

SUMMARY

The Centers for Disease Control and Prevention currently recommends syphilis screening with a nontreponemal test. However, as laboratories continue to implement the reverse screening algorithm, it is important that samples with discordant screen-reactive, RPR-nonreactive results be tested by a second treponemal assay to assist in the interpretation of results.

It is time to use treponema-specific antibody screening tests for diagnosis of syphilis

Assays that detect treponema-specific antibodies, which are either automated or can be done as point-of-care tests, have been developed, some of which are FDA approved. These assays have the advantage of being easily performed and demonstrate high sensitivity, both key features of an infectious disease screening test. As a result, many high-volume clinical laboratories have begun to offer a reverse syphilis testing algorithm where a treponema-specific test is used for screening, followed by a nontreponemal test (i.e., rapid plasma reagin [RPR]) to assess disease activity and treatment status. Concerns about physicians being able to understand and apply this new testing algorithm have been expressed (8). In this point-counterpoint, Michael Loeffelholz of the University of Texas Medical Branch at Galveston explains why his laboratory has adopted this reverse algorithmic approach. Matthew Binnicker of the Mayo Clinic, Rochester, MN, explains why the reverse algorithm may not be suitable for all clinical laboratories and every clinical situation.

Early syphilis in a man with a negative Treponema pallidum enzyme immunoassay-IgM

Most serological tests for syphilis rely on an individual's ability to produce antibodies. A single screening test may be unreliable for screening in those with primary immunodeficiency. We present the first reported case of primary and secondary syphilis with negative Treponema pallidum enzyme immunoassay-IgM and Venereal Disease Research Laboratory tests in a man with common variable immunodeficiency.

Identification of false-positive syphilis antibody results using a semiquantitative algorithm

Screening patients for syphilis serology using a "treponemal assay-first" approach presents unique challenges, particularly when applied to low-prevalence populations. The use of a screening algorithm that incorporates semiquantitative values from treponemal antibody test results can help to identify potential false-positive results while requiring a minimum of repeat testing.

Characterization of Treponema pallidum particle agglutination assay-negative sera following screening by treponemal total antibody enzyme immunoassays

Following a laboratory audit, a significant number of Treponema pallidum particle agglutination assay (TPPA)-negative sera were identified when TPPA was used as a confirmatory assay of syphilis enzyme immunoassay (EIA) screening-reactive sera (SSRS). Sera giving such discrepant results were further characterized to assess their significance. A panel of 226 sera was tested by the Abbott Murex ICE Syphilis EIA and then by the Newmarket Syphilis EIA II. TPPA testing was performed on 223 sera. Further testing by the Venereal Disease Research Laboratory (VDRL) test, the Mercia Syphilis IgM EIA, the fluorescent treponemal antibody (FTA-ABS) assay, and INNO-LIA immunoblotting was undertaken in discrepant cases. One hundred eighty-seven of 223 (83.8%) SSRS were TPPA reactive, while 26 (11.6%) sera which were reactive in both the ICE and Newmarket EIAs were nonreactive by TPPA. The majority (68%) of the TPPA-discrepant sera were from HIV-positive patients and did not represent early acute cases, based on previous or follow-up samples, which were available for 22/26 samples. FTA-ABS testing was performed on 24 of these sera; 14 (58.3%) were FTA-ABS positive, and 10 (41.7%) were FTA-ABS negative. Twenty-one of these 26 sera were tested by INNO-LIA, and an additional 4 FTA-ABS-negative samples were positive. In this study, significant numbers (18/26) of SSRS- and TPPA-negative sera were shown by further FTA-ABS and LIA (line immunoblot assay) testing to be positive. The reason why certain sera are negative by TPPA but reactive by treponemal EIA and other syphilis confirmatory assays is not clear, and these initial findings should be further explored.

Evaluation of the Bio-Rad BioPlex 2200 syphilis multiplex flow immunoassay for the detection of IgM- and IgG-class antitreponemal antibodies

The laboratory diagnosis of syphilis is based primarily upon serologic findings. Historically, serologic testing for syphilis has relied on assays such as rapid plasma reagin, fluorescent treponemal antibody absorption, Treponema pallidum particle agglutination (TP-PA), and more recently, enzyme immunoassay (EIA). In this study, we evaluated the performance of a novel multiplex flow immunoassay (BioPlex 2200 Syphilis; Bio-Rad Laboratories, Hercules, CA) for the detection of antitreponemal IgG- and IgM-class antibodies. Serum specimens (n = 1,008) submitted for routine treponema-specific antibody testing by syphilis IgM and IgG EIA (Trep-Chek; Phoenix-Biotech, Mississauga, Ontario, Canada) were also analyzed by the BioPlex Syphilis multiplex assay. Specimens showing discordant results were repeat tested, with further discrepancies being arbitrated by TP-PA. Compared directly to the results of EIA, the BioPlex IgG assay demonstrated 98.7% (77/78) sensitivity and 99.4% (916/930) specificity. Compared to the Trep-Chek IgM EIA, the BioPlex IgM assay showed 80% (4/5) sensitivity and 97.9% (652/666) specificity. These results indicate that the BioPlex Syphilis multiplex assay shows similar serological agreement with EIA while allowing for a fully automated random-access platform that provides faster (1.7 h for 100 samples versus 4.5 h by EIA) and higher-throughput (800 samples per 9 h versus 200 samples by EIA) analysis of the syphilis serologic response.

Immunoassays for the diagnosis of HIV: meeting future needs by enhancing the quality of testing

Immunoassays for detecting HIV infection perform better than other serological assays. HIV immunoassays are presented in a number of different formats: instrument-based, plate, rapid assays and as immunoblots. HIV immunoassays for screening and diagnosis are now in their fourth generation; an assay generation meaning that significant modifications to the assay format have led to a significant enhancement in quality. Although still not perfect, they are now of exceptionally high quality if conducted properly. Most problems relate to how the assays are performed. Many laboratories, especially in high human development index (HDI) countries, manage testing within functioning quality-management systems, but this is not true of laboratories in low HDI countries or in many medium HDI countries. Simple rapid tests for HIV are being used increasingly, and create special challenges for assuring quality. Users of HIV immunoassays are learning that a poorer assay used well has better outcomes than a splendid assay performed poorly. Experience highlights the importance of conducting HIV testing within quality-managed systems and according to international standards, but testing quality and laboratory quality management must be funded adequately.

Serological diagnosis of syphilis: enzyme-linked immunosorbent assay to measure antibodies to individual recombinant Treponema pallidum antigens

We standardized an indirect ELISA for measurement of serum antibody levels to four individual treponemal recombinant proteins that have been commonly used in a number of commercial EIAs, mostly as a mixture of antigens. When tested with 127 syphilis-negative and 37 secondary syphilis sera, ELISA O.D.s obtained for each of the four antigens clearly distinguished between these two groups of samples. Sensitivity and specificity of 100% was obtained with the current set of samples. Further evaluations with sera from different stages of syphilis can help to define the applications of this ELISA test for each of the four antigens studied.