The serological diagnosis of syphilis is classified into two groups: Nontreponemal tests (RPR/VDRL) and Treponemal tests (TPHA/CLIA). Syphilis serology is a treponemal assay for the qualitative determination of antibodies to T. pallidum in human serum or plasma as an aid in the diagnosis of syphilis. Treponemal tests may remain reactive for life, even following adequate therapy thus a positive result suggests infection with Treponema pallidum but does not distinguish between treated and untreated infections. Therefore, the results of a nontreponemal assay, such as rapid plasma reagin, are needed to provide information on a patient's disease state and history of therapy. Nontreponemal tests lack sensitivity in late stage of infection and screening with these tests alone may yield false positive reactions in various acute and chronic conditions in the absence of syphilis (biological false positive reactions).