dev exp health med

Developments and Experiments in Health and Medicine

3062-2948

Dokuz Eylul University

10.18614/dehm.1772212

Infectious Diseases Clinical Microbiology

Bulaşıcı Hastalıklar Klinik Mikrobiyoloji

Reverse syphilis screening algorithm in a high-volume laboratory: CLIA–RPR–TPHA concordance and determinants of RPR reactivity

https://orcid.org/0000-0003-3953-5267

Gülmez

Abdurrahman

Aydin Ataturk State Hospital, Medical Microbiology Laboratory

https://orcid.org/0000-0002-6726-0048

Kömeç

Selda

Istanbul Basaksehir Cam and Sakura City Hospital, Medical Microbiology Laboratory

04 29 2026

40 2 210 219 08 26 2025 12 02 2025

2025

Developments and Experiments in Health and Medicine

Objective: Syphilis remains a major global health concern, with an estimated 8 million new infections annually. The reverse syphilis screening algorithm, which starts with a treponemal assay followed by a non-treponemal test, has gained wide adoption in diagnostic laboratories. Despite its advantages, the interpretation of discordant results and the factors influencing RPR reactivity in real-world practice are not fully understood. This study aimed to evaluate the diagnostic concordance between CLIA, RPR, and TPHA assays and to identify demographic and clinical factors associated with RPR reactivity in a high-volume tertiary laboratory. Methods: A retrospective analysis was performed on 109,390 serum samples tested between January 2021 and January 2023. CLIA-reactive samples underwent RPR testing and, when indicated, TPHA confirmation. Logistic regression analysis was used to determine predictors of RPR positivity, and receiver operating characteristic (ROC) analysis evaluated the performance of CLIA signal-to-cutoff (S/CO) ratios in predicting TPHA positivity. Results: Among 995 (0.91%) CLIA-reactive samples, 278 (29.4%) were RPR-positive. TPHA testing confirmed 76 (64.4%) of 118 RPR-negative samples as true positives. Younger age and outpatient status were independent predictors of RPR reactivity (adjusted OR for 18–45 years: 3.39, 95% CI: 2.10–5.48, p<0.001; outpatient vs. inpatient: OR 2.17, 95% CI: 1.47–3.19, p<0.001). A strong correlation was observed between CLIA and TPHA (ρ=0.706, p<0.001), whereas the CLIA–RPR correlation was weak (ρ=0.084, p=0.161). ROC analysis yielded an AUC of 0.964, with an optimal CLIA S/CO threshold of 18.3 (100% sensitivity, 85.7% specificity). Conclusion: The reverse syphilis screening algorithm demonstrated excellent diagnostic performance and high concordance between CLIA and TPHA assays. RPR reactivity was largely influenced by age and clinical setting, emphasizing the importance of integrating demographic context into serologic interpretation. CLIA can serve as a robust primary screening tool in high-throughput laboratories, complemented by RPR and TPHA for accurate staging and confirmation.

Immunoassay public health receiver operating characteristic curve analysis retrospective studies serological tests syphilis

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