Performance Assessment of Treponemal and Nontreponemal Tests for the Diagnosis of Acquired Syphilis.

There are a variety of nontreponemal test (NTT) and treponemal test (TT) kits for the serologic diagnosis of syphilis. Because of the complexity of the infection (multiple clinical stages) and the different antigens used in these kits, a systematic evaluation of the accuracy of the currently available commercial tests is warranted. Our objective was to evaluate the performance of commercially available tests for the diagnosis of syphilis infection. In this study, we analyzed one NTT (Venereal Disease Research Laboratory [VDRL] test, Wiener Laboratories, Rosario, Argentina) and two TTs (fluorescent treponemal antibody absorption [FTA-ABS] test, Euroimmun, Lübeck, Germany, and syphilis recombinant ELISA v. 4.0 test [ELISA], Wiener Laboratories, Rosario, Argentina) using a panel of 187 samples, including serum samples from 31 individuals with primary syphilis, 77 with secondary syphilis, and 79 with latent syphilis. An additional 192 samples from uninfected individuals and 323 serum samples from individuals with other diseases were included. The sensitivities of the VDRL, ELISA, and FTA-ABS tests were 97.9%, 100%, and 96.3%, respectively. The VDRL and ELISA tests showed a specificity of 100%, and the FTA-ABS test showed a specificity of 99.5%. Accuracy was 98.9% for the VDRL test, 100% for the ELISA, and 97.9% for the FTA-ABS test. For primary, secondary, and latent syphilis, the ELISA achieved a diagnostic performance of 100%, whereas the sensitivity for the VDRL and FTA-ABS tests ranged from 96.8% to 98.7% and 93.7% to 98.7%, respectively. No difference was observed when the tests were used as traditional or reverse algorithms. In general, all three tests are able to discriminate positive and negative samples for syphilis, regardless of the diagnostic algorithm.

External quality assessment to support the WHO ProSPeRo study for the evaluation of two dual HIV/syphilis point-of-care tests in seven countries.

BACKGROUND: Sexually transmitted infections (STIs) such as syphilis and HIV remain to be a significant public health issue worldwide. Dual rapid point-of-care tests (POCTs) have shown promise for detecting antibodies to HIV and syphilis but have not been fully evaluated in the field. Our study supported the WHO ProSPeRo study on Sexually Transmitted Infection Point-of-Care Testing (STI POCT) by providing external quality assessment (EQA) for HIV and syphilis testing in reference laboratories and their associated clinical sites in seven countries. METHODS: HIV/syphilis serum liquid and dried tube specimen (DTS) panels were prepared by CDC. Liquid panels were distributed to the reference laboratories for three rounds of testing using commercially and locally available laboratory-based serological tests. DTS panels were sent to the clinical testing sites for 8 rounds of POC testing using the Abbott SD BIOLINE HIV/Syphilis Duo test (hereafter referred to as SD BIOLINE) and the Chembio Dual Path Platform (DPP) HIV-Syphilis assay. EQA panels were tested at CDC using the Rapid Plasma Reagin (RPR) test and the Treponema pallidum Particle Agglutination assay (TP-PA) for syphilis antibodies. Genetic Systems HIV-1/HIV-2 Plus O EIA, Geenius HIV Supplemental Assay and the Oraquick Advance HIV test were used to detect HIV antibodies in the EQA panels. Results from the reference laboratories and POCT sites were compared to those obtained at the CDC and a percentage agreement was calculated. RESULTS: Qualitative RPR and TP-PA performed at the reference laboratories demonstrated 95.4-100% agreement with CDC results while quantitative RPR and TP-PA tests demonstrated 87.7% and 89.2% agreement, respectively. A 93.8% concordance rate was observed for qualitative HIV testing in laboratories. EQA testing at clinical sites using dual tests showed 98.7% and 99.1% agreement for detection of HIV antibodies and eight out of 10 sites had > 95.8% agreement for syphilis testing. However, two clinical sites showed only 65.0-66.7% agreement for SD BIOLINE and 84.0-86.7% for DPP, respectively, for syphilis testing. CONCLUSIONS: Overall, laboratories demonstrated high EQA performance in this study. Both HIV/syphilis POCTs gave expected results in the clinic-based evaluations using DTS. However, testing errors were identified in a few testing sites suggesting the necessity for continuous training and monitoring the quality of POC testing.

Inmunoanálisis quimioluminiscente de micropartículas (CMIA) en el diagnóstico de sífilis: caracterización y valorización / Chemioluminescent microparticle immunoanalysis (CMIA) in the diagnosis of syphilis: characterization and assessment

INTRODUCCIÓN: La inmunoquimioluminiscencia de micropartículas (CMIA), no es recomendada en el día de hoy para el tamizaje ni confirmación de sífilis en pacientes, las guías chilenas recomiendan tamizaje con V.D.R.L y confirmación con hemaglutinación. OBJETIVO: Determinar la especificidad, sensibilidad y correlación diagnóstica de esta técnica respecto a la prueba treponémica de uso habitual. MATERIALES Y MÉTODOS: De 815 muestras obtenidas en un periodo de 6 meses, a todas las cuales se les aplicó las pruebas de VDRL, MHA-TP y CMIA, 484 muestras fueron positivas para MHA-TP. Se determinó el rendimiento, se graficaron las curvas ROC, índice de correlación y punto de corte óptimo. RESULTADOS: La CMIA. demostró una sensibilidad de 100%, especificidad: 94,6%, VPN: 100% y VPP: 96.4% y una eficiencia de 97,8% con respecto al MHA-TP, con un índice de correlación: 0,97 y un punto de corte de 7.665, de modo que toda muestra con una CMIA. sobre este valor no necesitaría de una segunda prueba treponémica para su confirmación. El 7,11% tuvo valores intermedios de CMIA (1.0 a 7.664). CONCLUSIÓN: La CMIA. es una técnica automatizada altamente sensible y específica, equiparable al MHA-TP. Aplicada como prueba inicial de testeo para sífilis incrementa la certeza diagnóstica y podría permitir el diagnóstico precoz de la enfermedad.

BACKGROUND: The chemiluminescent microparticle immunoassay (CMIA) is not recommended for screening or confirmation of syphilis in patients, Chilean guidelines recommend screening with VDRL and confirmation with hemagglutination. AIM: To determine the specificity, sensitivity, and diagnostic correlation of this technique compared to the usual treponemal test. METHODS: Of the 815 samples obtained over a period of 6 months, all of which were subjected to VDRL, MHATP, and CMIA. testing, 484 samples were positive for MHA-TP. The performance was determined, ROC curves were graphed, correlation index and optimal cutoff point were determined. RESULTS: CMIA showed a sensitivity of 100%, specificity of 94.6%, NPV of 100%, PPV of 96.4%, and an efficiency of 97.8% compared to MHA-TP, with a correlation index of 0.97 and a cutoff point of 7.665, such that any sample with a CMIA. value above this value would not require a second treponemal test for confirmation. 7.11% had intermediate CMIA. values (1.0 to 7.664). CONCLUSION: CMIA. is a highly sensitive and specific automated technique comparable to MHA-TP. When applied as an initial screening test for syphilis, it increases diagnostic certainty and may allow for early diagnosis of the disease.

Assessment of a fully automated RPR assay (Mediace RPR) for serological diagnosis and follow-up of syphilis: a retrospective study.

OBJECTIVES: This study assessed the Mediace RPR assay, an automated RPR (aRPR), for syphilis diagnosis and serological follow-up. METHODS: Serums from patients positively screened for syphilis between January 2017 and December 2019 were retrospectively selected. A focus was performed on patients with a serological follow-up after treatment and/or a reinfection. Serums were tested by both manual (mRPR) and aRPR tests. Categorical and Quantitative Agreements (CA and QA), and serological follow-up conclusions were analyzed. RESULTS: 236 serums from 85 patients (99% of male, 66% of HIV-infected) were included. The overall QA was 54.2%. CA was low (79.7%) especially for samples with low RPR titers. No prozone effect was observed. Serological follow-up after treatment led to similar conclusions, although aRPR titers often decreased faster. Over 26 episodes of reinfection, 4 (15.4%) were misdiagnosed with the aRPR. CONCLUSIONS: While the Mediace aRPR presents the advantages of an automated test, its poor sensitivity in low titers may limit its use.

Assessment of recombinant antigens Tp0100 and Tp1016 of Treponema pallidum for serological diagnosis of syphilis.

OBJECTIVE: To discover novel serodiagnostic candidates for the serological diagnosis of syphilis. METHODS: Two recombinant Treponema pallidum proteins Tp0100 and Tp1016 were expressed, purified, and identified by Western Blotting. A total of 600 clinical serum samples were tested with the Tp0100-based ELISA, the Tp1016-based ELISA, and the commercial LICA Syphilis TP kit (ChIVD, Beijing, China). The sensitivities were determined by testing 340 samples from individuals with clinically diagnosed primary, secondary, latent, and tertiary syphilis. The specificities were determined by screening 260 samples from healthy controls and individuals with potentially cross-reactive infections, including leptospirosis, Lyme disease, hepatitis B, tuberculosis, rheumatoid arthritis, systemic lupus erythematosus. Kappa (κ) values were applied to compare the agreement between clinical syphilis diagnosis and the Tp0100-based ELISA, the Tp1016-based ELISA, or the LICA Syphilis TP test. RESULTS: Using clinical syphilis diagnosis as the gold standard, Tp0100 exhibited an overall sensitivity of 95.6% and specificity of 98.1% for testing IgG antibody while Tp1016 demonstrated only an overall sensitivity of 75.0% and specificity of 79.6%. In contrast, the LICA Syphilis TP test revealed an overall sensitivity of 97.6% and specificity of 96.2%. In addition, the overall percent agreement and corresponding κ values were 96.7% (95% CI 95.6%-97.8%) and 0.93 for the Tp0100-based ELISA, 77.0% (95% CI 74.3%-79.7%) and 0.54 for the Tp1016-based ELISA, and 97.0% (95% CI 96.0%-98.0%) and 0.94 for the LICA Syphilis TP test, respectively. CONCLUSION: The recombinant T. pallidum protein Tp0100 shows promise as a novel diagnostic antigen in the serological tests for syphilis.

Costs of Identifying Cases of Syphilis Using Rapid Syphilis Tests in Multiple Nonclinical Settings in the United States.

BACKGROUND: Outreach screening is a common strategy for detecting cases of syphilis in high-risk populations. New rapid syphilis tests allow for quicker response times and may alter the costs of detecting and treating syphilis in nonclinical settings. METHODS: Between May and October of 2017, we collected detailed retrospective cost data from 2 outreach screening programs engaging people experiencing homelessness and LGBTQ populations. Comprehensive and retrospective cost information, disaggregated by cost category, programmatic activity, and source of support, was collected during and after the testing period. RESULTS: Across all sites, rapid syphilis tests were conducted on 595 people at an average cost of $213 per person. Twenty-three cases of syphilis were confirmed and treated for an average cost of $5517 per case, ranging from $3604 at a rehabilitation facility to $13,140 at LGBTQ venues served by a mobile clinic. Personnel contributed the most to total costs (56.4%), followed by supplies (12.8%) and the use of buildings (10.4%). Expenditures by programmatic activity varied substantially across sites. CONCLUSIONS: Testing costs varied between venues, reflecting differences in the models used and intensity of services provided. Although staff costs are the major driver, buildings and supplies costs are also significant. Our findings suggest that outreach screenings using rapid syphilis tests may be a feasible and cost-effective tool for health departments when targeting known high-prevalence areas and hard-to-reach populations.

The impact of antenatal syphilis point of care testing on pregnancy outcomes: A systematic review.

BACKGROUND: Mother-to-child transmission of syphilis remains a leading cause of neonatal death and stillbirth, disproportionally affecting women in low-resource settings where syphilis prevalence rates are high and testing rates low. Recently developed syphilis point-of-care tests (POCTs) are promising alternatives to conventional laboratory screening in low-resource settings as they do not require a laboratory setting, intensive technical training and yield results in 10-15 minutes thereby enabling both diagnosis and treatment in a single visit. Aim of this review was to provide clarity on the benefits of different POCTs and assess whether the implementation of syphilis POCTs is associated with decreased numbers of syphilis-related adverse pregnancy outcomes. METHODS: Following the PRISMA guidelines, three electronic databases (PubMed, Medline (Ovid), Cochrane) were systematically searched for intervention studies and cost-effectiveness analyses investigating the association between antenatal syphilis POCT and pregnancy outcomes such as congenital syphilis, low birth weight, prematurity, miscarriage, stillbirth as well as perinatal, fetal or infant death. RESULTS: Nine out of 278 initially identified articles were included, consisting of two clinical studies and seven modelling studies. Studies compared the effect on pregnancy outcomes of treponemal POCT, non-treponemal POCT and dual POCT to laboratory screening and no screening program. Based on the clinical studies, significantly higher testing and treatment rates, as well as a significant reduction (93%) in adverse pregnancy outcomes was reported for treponemal POCT compared to laboratory screening. Compared to no screening and laboratory screening, modelling studies assumed higher treatment rates for POCT and predicted the most prevented adverse pregnancy outcomes for treponemal POCT, followed by a dual treponemal and non-treponemal POCT strategy. CONCLUSION: Implementation of treponemal POCT in low-resource settings increases syphilis testing and treatment rates and prevents the most syphilis-related adverse pregnancy outcomes compared to no screening, laboratory screening, non-treponemal POCT and dual POCT. Regarding the benefits of dual POCT, more research is needed. Overall, this review provides evidence on the contribution of treponemal POCT to healthier pregnancies and contributes greater clarity on the impact of diverse diagnostic methods available for the detection of syphilis.

The Traditional or Reverse Algorithm for Diagnosis of Syphilis: Pros and Cons.

We reviewed relevant syphilis diagnostic literature to address the question "What diagnostic considerations should be taken into account when screening for syphilis using the traditional or reverse algorithm?" Improved laboratory diagnosis of syphilis is an important element of the effort to reduce syphilis rates. Screening for syphilis is performed using either a nontreponemal or treponemal test (part of the traditional or reverse algorithm, respectively). Both syphilis algorithms are used by laboratories. However, there are limited data on the performance and cost-effectiveness of the algorithms. An expert panel generated "key questions" in the laboratory diagnosis of syphilis. This paper pertains to the key factors that should be considered when deciding whether to screen for syphilis using either the traditional or the reverse algorithm. A systematic literature review was performed, and tables of evidence were created to address this question.

Laboratory assessment of SD Bioline HIV/Syphilis Duo Kit among pregnant women attending antenatal clinic Mayuge Health Center III, East central Uganda.

OBJECTIVE: Efforts to dual eradication of mother-to-child transmission of human immune deficiency virus (HIV) and syphilis have improved in the previous decades. This has however been hindered by limited validation studies. A cross-sectional study was conducted among adult pregnant women attending antenatal care clinic at Mayuge Health Center III. Two milliliters of venous blood were collected into Ethylene di-amine tetra acetic acid vacutainers, and tested for HIV and syphilis using the SD Bioline HIV/Syphilis Duo assay, and the national HIV and syphilis testing algorithm. Sensitivity and specificity were calculated for the Duo Kit against the gold standards within 95% confidence intervals. RESULTS: Three hundred and eighty-two (382) participants were enrolled. Their mean age was 25.8 years. The prevalence of HIV was 1.8% (95% confidence interval 1.23-2.41); while that of syphilis was 2.1% (95% confidence interval 1.81-2.54), and the dual infection was 0.52% (95% confidence interval 0.37-0.92). The sensitivity and specificity of the SD Bioline HIV/Syphilis Duo assay were all 100.0% (95% confidence interval 99.5 to 100.0 and 98.6 to 100.0, respectively). The performance of the SD Bioline HIV/Syphilis Duo Kit was optimal, reassuring its aptness for use, and favorable qualities to a limited resource setting.

Congenital Syphilis: A Discussion of Epidemiology, Diagnosis, Management, and Nurses' Role in Early Identification and Treatment.

BACKGROUND: Syphilis is caused by the spirochete bacterium Treponema pallidum. Syphilis left untreated, or inadequately treated during pregnancy, can result in congenital syphilis (CS). Congenital syphilis can lead to severe sequelae or fetal, neonatal, or infant death. PURPOSE: To discuss the epidemiological trends, pathophysiology, diagnosis, and management of CS; the implications of CS upon the infant; as well as the importance of the nurse's role in the prompt identification of CS and the timely interventions needed to minimize sequelae. METHODS: A literature search was completed using ProQuest, CINAHL, Google Scholar, and PubMed. Articles published within the past 10 years were included. FINDINGS: Epidemiological trends of CS in the United States indicate that maternal syphilis infection and CS are on the rise. Risk factors include ethnicity, socioeconomic status, access to prenatal care, and sexual behaviors, as well as compliance with prenatal syphilis screening by prenatal providers. Risks of CS to the developing fetus begin at approximately 14 weeks. Timely treatment is necessary to minimize or eliminate mortality and morbidity. IMPLICATIONS FOR PRACTICE: Evidence-based, interprofessional strategies, which promote a collaborative perinatal/neonatal preventative approach to care of the pregnant female, are indicated to reverse the increasing incidence of CS within the United States. Strategies prioritizing early identification and treatment of at-risk neonates are necessary to reduce/eliminate the devastating long-term consequences of CS upon this vulnerable population. IMPLICATIONS FOR RESEARCH: The paucity of research, which focuses on CS, is most likely due to ethical concerns related to infants as research participants and provides an opportunity for future research. Future research could focus on factors that focus on maternal-fetal/maternal-child transmission of CS.

Economic Assessment of Reverse Algorithm Syphilis Screening in a High Prevalence Population.

BACKGROUND: More laboratories are screening for syphilis with automated treponemal immunoassays. We compared direct costs and downstream consequences when a local public health laboratory switches from a traditional algorithm (nontreponemal screening) to a reverse algorithm (treponemal screening). METHODS: We created a decision analysis model based on laboratory and surveillance data to estimate the cost-effectiveness of a reverse syphilis-screening algorithm from the perspectives of the Los Angeles County Public Health Laboratory and the Los Angeles County Department of Public Health (laboratory + STD Program costs) in 2015 US dollars. RESULTS: The estimated total costs for the Department (Public Health Laboratories) were $2,153,225 ($367,119) for the traditional algorithm and $2,197,478 ($239,855) for the reverse algorithm. Reverse algorithm screening was estimated to detect an additional 626 cases of syphilis, 9.7% more than the traditional algorithm. The incremental cost-effectiveness ratio for the reverse algorithm from the Public Health Department's perspective was $39 per additional syphilis case detected. Cost of follow-up, screening test costs, positivity rates, and frequency of repeat infections most affected the cost-effectiveness of reverse algorithm. Costs were significantly higher for the reverse algorithm when the enzyme Immunoassay/chemiluminescence immunoassay screening test cost was the same as the published Centers for Medicaid Services treponemal test cost. CONCLUSIONS: Using the reverse algorithm would have been slightly more expensive for the Los Angeles County Department of Public Health, but would have identified more syphilis cases and would have resulted in lower laboratory costs.

Monetary incentives for provision of syphilis screening, Yunnan, China.

PROBLEM: Early detection of syphilis-infected people followed by effective treatment is essential for syphilis prevention and control. APPROACH: Starting in 2010 the local health authority in Yunnan province, China, developed a network of 670 service sites for syphilis testing, diagnosis and treatment or for testing-only with referral for further diagnosis and treatment. Point-of-care tests for syphilis and syphilis interventions were integrated into the existing human immunodeficiency virus (HIV) prevention and control programme. To improve the syphilis services, a pay-for-performance scheme was introduced in which providers were paid for testing and treating patients. LOCAL SETTING: Yunnan province is the region hardest hit by HIV infection and disproportionately burdened with syphilis cases in China. RELEVANT CHANGES: The proportion of attendees at voluntary counselling and testing clinics who were tested for syphilis increased from 46.2% (32 877/71 162) in 2010 to 98.2% (68 012/69 259) in 2015. Syphilis-infected cases treated with the recommended therapy increased from 26.6% (264/993) in 2010 to 82.5% (453/549) in 2015 at designated testing, diagnosis and treatment sites. LESSONS LEARNT: The strategy greatly increased the uptake of syphilis testing and treatment among people at risk. Introduction of point-of-care tests for syphilis increased coverage of the testing services. Introduction of a pay-for-performance scheme seemed to motivate health-care providers to undertake syphilis intervention services.

Maternal Syphilis: An Independent Risk Factor for Mother to Infant Human Immunodeficiency Virus Transmission.

Syphilis is associated with increased human immunodeficiency virus acquisition and sexual transmission; we examined impact on human immunodeficiency virus mother-to-child transmission among mother-infant pairs enrolled in the India Six-Week Extended-Dose Nevirapine study. Maternal syphilis, diagnosed serologically using Venereal Disease Research Laboratory titer plus Treponema Pallidum Hemagglutination Assay, was associated with 2.5-fold greater risk.

Suboptimal Prenatal Syphilis Testing Among Commercially Insured Women in the United States, 2013.

United States surveillance data demonstrate that congenital syphilis cases are increasing. We performed an analysis of commercially insured pregnant females using MarketSan to determine syphilis screening rates at different prenatal stages; 85% of pregnant women in this population had a syphilis test performed at least once during the prenatal period.

Improving the antenatal and post-partum management of women presenting to Sexual Health Services with positive syphilis serology through audit.

The incidence of congenital syphilis remains low in the UK, but the morbidity and mortality to babies born to women who are untreated for the condition make testing for the disease antenatally one of the most cost-effective screening programmes. Women attending North Middlesex Hospital, UK with a positive syphilis test at their antenatal booking visit are referred to St Ann's Sexual Health Clinic, London, for management and contact tracing. We were concerned that our initial audit revealed that a large proportion of women referred to our service never attended and recorded partner notification was poor. Following the implementation of recommendations, specifically the introduction of an electronic referral system, re-audit showed an improvement in attendance, contact tracing, documentation and communication.

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.

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.