title: Improved reverse screening algorithm for Treponema pallidum antibody using signal-to-cutoff ratios from chemiluminescence microparticle immunoassay.
abstract: BACKGROUND
  The widespread reverse syphilis screening algorithm involves 1 more treponemal test than the traditional screening algorithm, resulting in increased medical costs. In the first screening step of the algorithm, a chemiluminescence microparticle immunoassay is used to detect Treponema pallidum (TP) antibody on the basis of signal-to-cutoff (S/CO) ratios. We hypothesized that by analyzing S/CO ratios, we could determine a strategy to reduce unnecessary confirmatory testing.
  
  
  METHODS
  The ARCHITECT Syphilis TP assay using the chemiluminescence microparticle immunoassay was used as a syphilis screening test, and all reactive results were followed up with a toluidine red unheated serum test (TRUST) and a TP particle agglutination (TPPA) assay. We evaluated the S/CO ratios of 319 reactive samples of a total of 8980 that were included in the screening tests. A receiver operating characteristic curve was used to determine the optimal S/CO ratio to predict confirmatory TPPA results.
  
  
  RESULTS
  When the S/CO ratio was 9.9 or greater, the specificity and positive predictive value were both determined to be 100.0%. All samples (194/194) with S/CO ratios of 9.9 or greater, even with negative results for TRUST, were confirmed to be positive for treponemal antibody.
  
  
  CONCLUSIONS
  A sample with an S/CO ratio of 9.9 or greater in initial screening does not need an extra confirmatory TPPA test, although the sample has a negative result for TRUST. We propose a potentially cost-effective reverse screening algorithm, obviating the need for the secondary treponemal testing in 65.2% of the screening-reactive samples.
authors: From the *State Key Laboratory of Oncology in South China and Departments of †Clinical Laboratory and ‡Thoracic Surgery, Sun Yat-sen University Cancer Center, Guangzhou, Guangdong, China.
authors: Shuqin
authors: S
authors: Dai
authors: Peidong
authors: P
authors: Chi
authors: Yuehao
authors: Y
authors: Lin
authors: Xin
authors: X
authors: Zheng
authors: Wen
authors: W
authors: Liu
authors: Jingping
authors: J
authors: Zhang
authors: Qiuyao
authors: Q
authors: Zeng
authors: Xingping
authors: X
authors: Wu
authors: Wanli
authors: W
authors: Liu
authors: Junye
authors: J
authors: Wang
mesh_terms: D000465:Algorithms; D000907:Antibodies, Bacterial / Q000302:isolation & purification; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D008163:Luminescent Measurements; D008297:Male; D008403:Mass Screening / Q000379:methods*; D012680:Sensitivity and Specificity; D013587:Syphilis / Q000175:diagnosis* / Q000276:immunology; D014210:Treponema pallidum / Q000276:immunology / Q000302:isolation & purification*
chemical_list: D000907:Antibodies, Bacterial