Clinical Development and Performance of the First To Know Syphilis Self-Test for Over-the-Counter Usage: a De Novo Rapid Test for Treponemal Antibody

The resurgence of syphilis in the USA and globally has hastened the need for widely available syphilis testing. Early detection of syphilis is crucial for avoiding serious clinical complications and preventing spread of infection. Self-tests enhance access to testing and promote timely treatment for positive cases. Herein we describe the performance of First to Know Syphilis Test (FTK), the first over the counter (OTC) treponemal test. A prospective multi-site clinical study with 1270 subjects was conducted, where subjects self-collected fingerstick capillary blood and self-tested without assistance. FTK test results were compared with a composite reference standard to evaluate diagnostic performance. The FTK test exhibited an overall sensitivity of 93.4% (95% CI, 87.0% to 96.8%) and specificity of 99.5% (95% CI, 98.9% - 99.8%) and accuracy of 99%. The overall agreement was 98.9%, with Cohens Kappa (ⱪ) value 0.93 (95% CI, 0.90 to 0.97) showing excellent agreement between the reference standard and FTK results. In addition, the test was validated in a panel of 125 clinically staged syphilis patient samples and the results showed 100% agreement in detecting anti-treponemal antibodies in all the samples. These data show excellent performance of the FTK Test demonstrating its utility in the screening and diagnosis of syphilis. The availability of this OTC test and its excellent performance at low prevalence, will have a profound impact on syphilis detection and prevention strategies and could reduce co morbidities such as HIV and other STI transmission.