The end of the gold standard in syphilis diagnostics - A comparison of alternative screening test methods

BackgroundSyphilis can cause significant clinical complications in adults and severe harm to fetuses and newborns through vertical transmission if it remains undiagnosed and untreated. With syphilis being on the rise in many countries, it causes a high and increasing burden of disease worldwide. Due to its high sensitivity and specificity, the TPPA (Treponema pallidum particle agglutination test) is considered the gold standard in serological syphilis diagnostic. However, the production of TPPA by the world's only manufacturer has stopped which has generated major gaps in diagnostic capabilities.MethodsFour polyvalent screening tests from Abbott, Roche, Diasorin and Euroimmun were evaluated on the base of negative, borderline and positive samples to develop an alternative diagnostic procedure of the highest possible quality. Additionally, alternative diagnostic threshold values of the test systems were evaluated for further optimization.ResultsA total of 1768 samples from different patient populations were analyzed. When performed according to the manufacturer's instructions, most tests achieved a high specificity. However, the sensitivity of the screening tests was not fully satisfactory, particularly in the early stages of infection, where sensitivity remained relatively low.ConclusionsBy lowering threshold values, the sensitivity could be significantly increased allowing for some of the evaluated assays to reach a test quality comparable to the TPPA, which is particularly relevant for samples from patients with higher risk of acquiring STIs. Moreover, the results of the polyvalent screening assays could also be used to monitor treatment success and detect possible re-infections.