Utilization and performance of a rapid treponemal antibody test for diagnosis of syphilis in a high-risk population at an urban county hospital

BACKGROUND: Rapid detection of syphilis infection enables timely antibiotic treatment to prevent long-term complications and further transmission. We implemented a treponemal rapid lateral flow immunochromatographic test that was performed by trained clinical laboratory personnel on a 24/7 basis in an urban county hospital. METHODS: From March 2023 to February 2024, 461 rapid syphilis tests (RSTs) were performed on serum from 449 patients. Specimens were also tested by a conventional reverse algorithm beginning with an enzyme immunoassay (EIA), followed by a rapid plasma reagin (RPR) test, and when necessary, an additional treponemal test to resolve discordant results. RESULTS: Most patients (349, 77.7%) initially presented to the emergency department. The most common patient risk factors for syphilis were substance use disorder (51.9%) and unstable housing (42.8%). Compared to the reverse algorithm, RST sensitivity was 52.2%, specificity 98.2%, positive predictive value 83.7%, and negative predictive value 92.1%. After excluding 45 patients who had a documented prior history of syphilis, RST sensitivity was 83.3%, specificity 98.2%, positive predictive value 74.1%, and negative predictive value 99.0%. Nearly all of the 33 patients testing negative by the RST but positive by EIA were more likely to have been treated for a previous infection: 27 had a documented history of treatment and 30 had undetectable or low RPR titers (<1:2). The median RST turnaround time was 1.6 hours compared to 197.8 hours for reverse algorithm screening. CONCLUSIONS: RST is a useful option for high-risk patients in urban settings. Other testing methods are preferable for previously treated syphilis, and conventional follow-up testing is required to confirm results.