Comparison of Diagnostic Algorithms with Commercial Kits Used to Detect Syphilis Antibodies

Nowadays, especially in laboratories with high testing capacity, the widespread use of automated treponemal tests has increased the importance of algorithms used for syphilis serodiagnosis. In suspected syphilis cases, choosing the best algorithm is important from the aspect of diagnosis, treatment initiation, and treatment follow-up. In this study, we aimed to compare the diagnostic performance of traditional, reverse, and European Center for Disease Prevention and Control (ECDC) algorithms according to the clinical diagnosis of syphilis using rapid plasma reagin (RPR), chemiluminescence immunoassay (CLIA), and Treponema pallidum hemagglutination (TPHA) tests.

Between March 2023 and July 2023, a total of 297 patients from various units of our hospital, suspected of having syphilis, were included in the study. All samples were analyzed using RPR, CLIA, and TPHA tests, and three different algorithms were examined separately. Clinical diagnosis was considered the gold standard.

A total of 105 patients have been diagnosed with syphilis. When the patients' clinical diagnosis were used as a reference, the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the traditional algorithm were found to be 41.9%, 100%, 100% and 75.9%, respectively, and all these parameters were found to be 100% for the reverse and ECDC algorithms. Moderate agreement (kappa value 0.483, p < 0.001) was found between the traditional and reverse algorithms. Very good agreement (kappa value 1.0, p < 0.001) was found between ECDC and the reverse algorithm.

In diagnosing suspected syphilis cases, the reverse algorithm and ECDC algorithms utilizing treponemal tests as the initial step were found to be superior to the traditional algorithm. Our study demonstrates that treponemal antibody tests are superior when employed as the initial step in diagnosing syphilis in patients with latent syphilis among suspected cases. Nontreponemal tests should be used solely to evaluate disease activity and response to therapy.