title: Significance of isolated reactive treponemal chemiluminescence immunoassay results.
abstract: BACKGROUND
  Isolated reactive serum treponemal chemiluminescence immunoassay (CIA) specimens cause clinical uncertainty.
  
  
  METHODS
  Sera were screened by CIA, and reactive samples underwent reflex testing with rapid plasma reagin (RPR), Treponema pallidum particle agglutination (TPPA), and fluorescent treponemal antibody absorption (FTA Abs) assays. Samples reactive only on the CIA were deemed "isolated" reactive CIA samples. We undertook detailed review of a subset of subjects with isolated reactive CIA specimens.
  
  
  RESULTS
  Of 28 261 specimens, 1171 (4.1%) were reactive on CIA, of which 133 (11.3%) had isolated CIA reactivity. Most subjects (66 of 82 [80.5%]) with isolated reactive CIA specimens were from high-prevalence populations. We found evidence of CIA, TPPA, and FTA Abs seroreversion. The median chemiluminescent signal-to-cutoff ratio was similar for isolated reactive CIA sera and sera that were reactive on either FTA Abs or TPPA assays (2.19 vs 2.32; P = .15) but lower than for sera reactive on both FTA Abs and TPPA assays (12.37; P < .001) or for sera reactive on RPR assays (25.53; P < .001). A total of 11 of 20 patients (55%) with an isolated reactive CIA specimen who underwent medical record review had previous or subsequent evidence of syphilis infection.
  
  
  CONCLUSIONS
  Isolated reactive CIA specimens may represent true T. pallidum infection and may be found after seroreversion of traditional treponemal assays.
authors.affiliation: Department of Infectious Diseases and Albion Street Centre, Prince of Wales Hospital and Prince of Wales Clinical School, University of New South Wales, Randwick, Australia.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Hunter
authors.forename: Peter W
authors.initials: PW
authors.lastname: Robertson
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Post
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D049449:Luminescence; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D013587:Syphilis / Q000175:diagnosis*; D013588:Syphilis Serodiagnosis / Q000379:methods*; D014210:Treponema pallidum / Q000276:immunology*; D055815:Young Adult