Diagnostic Accuracy of RPR and TPHA Tests for Syphilis in Pregnant Women: A Study on Biological False Positives and Screening Efficacy

Background: Syphilis, caused by Treponema pallidum, remains a significant public health issue, particularly for pregnant women, with the potential to cause severe maternal and fetal complications, including stillbirth, preterm birth, low birth weight, and congenital syphilis. Early diagnosis and treatment are essential to prevent these adverse outcomes. Objective: This study aimed to assess the diagnostic accuracy of Rapid Plasma Reagin (RPR) and Treponema Pallidum Hemagglutination Assay (TPHA) tests in identifying syphilis in pregnant women and to evaluate the prevalence of biological false-positive results. Materials and Methods: A retrospective descriptive study was conducted from November 2023 to November 2024, involving 6,363 non-duplicate venous blood samples collected from antenatal care patients at PIMS Hospital. All samples were initially tested with the RPR test, and reactive cases were further tested using the TPHA. Data were analyzed using MedCalci software, with statistical significance set at a p-value of < 0.05. Results: Out of 6,363 samples, 109 (1.71%) were RPR reactive. These samples underwent semi-quantitative RPR testing at dilutions of 1:2, 1:4, 1:8, 1:16, 1:32, and 1:64. Higher dilutions (1:8 and above) showed a higher number of TPHA-positive cases, with 46 cases at dilutions >1:16. A total of 39 biological false-positive cases (0.61%) were identified in dilutions below 1:8. Among the 109 RPR reactive cases, the majority (73.39%) were in the 21-30 years age group, with 25.69% of false positives also occurring in this group. However, this age distribution was not statistically significant. Conclusion: Syphilis diagnosis in pregnancy requires a combination of RPR and TPHA tests to minimize false-positive results. Regular screening and early treatment are crucial to prevent syphilis-related complications. The study underscores the need for confirmatory testing in clinical practice to ensure accurate diagnosis and effective treatment, ultimately reducing maternal and neonatal morbidity and mortality associated with syphilis.