Performance of the Syphilis Serology Algorithm Diagnosis

Abstract

Abstract Syphilis is a chronic, sexually transmitted disease caused by Treponema pallidum. The clinical manifestations of syphilis are often non-specific. Serology tests are used for diagnosis. The aim of this study was to evaluate the reverse algorithm used at The Ohio State Wexner Medical Center (OSUWMC) for the diagnosis of syphilis. The algorithm consist of a treponemal test (Bio-Rad BioPlex Syphilis IgG) a multiplex flow immunoassay (MFI), which utilizes treponemal antigens coated on microspheres to detect IgG to T. pallidum. If reactive, a nontreponemal test, rapid plasma reagin (RPR), is used to detect antibodies against cardiolipin-cholesterol-lecithin antigens, though not specific they are present in most patients with syphilis. If results are reactive with MFI but nonreactive with RPR, a second treponemal-specific antibody test using T. pallidum particle agglutination (TP-PA) is used. Sera submitted at OSUWMC between 01/1/2013 and 10/13/2017 were tested for syphilis using the described algorithm. A total of 70,849 specimens were tested using the MFI assay, of these 96.5% were nonreactive (n= 68,394), 3.3% were reactive (n=2,318) and 0.2% produced an equivocal result (n= 137). Of the MFI reactive results, 1.5% confirmed reactive with RPR (n=1,031) and 1.8% (n=1,287) were nonreactive and considered discrepant. The discrepant specimens were tested by TP-PA, 0.6% (n=438) were confirmed nonreactive and 1.2 % (n=849) were reactive. Furthermore, 137 specimens that produced an equivocal result by the MFI were tested by RPR and TP-PA, 133 were nonreactive and 4 were reactive. In summary, only 2% (n=1,424) of the specimens were discrepant and required a third test for resolution.