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J Eur Acad Dermatol Venereol. 2019 Jan;33(1):178-184. doi: 10.1111/jdv.15251. Epub 2018 Oct 12.

Screening for syphilis with dual algorithms: analysis of discordant and concordant serology results in a population with a low prevalence of syphilis.

Zhuang YH1,2,3, Liu H3, Tang J3, Wang YZ3, Zheng XH4, Gong Y1,2, Xu XF1,2, Gao X1,2, Lu RQ1,2, Ju SG5, Guo L1,2.

Author information

1
Department of Clinical Laboratory, Fudan University Shanghai Cancer Center, Shanghai, China.
2
Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China.
3
Department of Laboratory Medicine, Shanghai Jiaotong University Affiliated Sixth People's Hospital, Shanghai, China.
4
Department of Laboratory Quality Management, Shanghai Municipal Centers for Disease Control and Prevention, Shanghai, China.
5
Department of Immunology, School of Biology and Basic Medical Sciences, Medical College, Soochow University, Suzhou, China.

Abstract

BACKGROUND:

Currently, many laboratories have switched the traditional screening algorithm (TSA) to reverse screening algorithm (RSA) for the efficiencies in high-volume syphilis screening. However, confusions have been arisen regarding this paradigm shift.

OBJECTIVE:

To compare the performance of two algorithms with head-to-head mode.

METHODS:

Sera screening for syphilis were tested in parallel with chemiluminescence immunoassay (CIA) and toluidine red unheated serum test (TRUST). CIA-reactive sera from the RSA were reflexively tested with TRUST and confirmed with Treponema pallidum particle agglutination assay (TPPA), while the TRUST-reactive serology from the TSA were afterwards tested with TPPA.

RESULTS:

A total of 110 663 serum samples were screened. The RSA identified 2259 (2.0%) CIA-reactive results, of which 377 (16.7%) showed TPPA nonreactive results, while the TSA identified 934 (0.8%) TRUST-reactive results, of which 67 (7.2%) showed TPPA-nonreactive results. Among the 2259 CIA-reactive results, 1392 (61.6%) were TRUST-nonreactive, of which 350 (25.1%) were TPPA-nonreactive. A total of 182 sera from the 350 TPPA-nonreactive sera were further tested by a second CIA (VITROS Syphilis TPA, VITROS TPA), of which 155 (85.2%) were nonreactive and 27 (14.8%) were reactive. The 27 VITROS TPA-reactive sera were further tested with a treponemal Western blot assay (Euroimmun IgG Western Blot, EuroWB), of which 11 (41%) were indeterminate, 6 (22%) were nonreactive and 10 (37%) were reactive. Among the 10 EuroWB-reactive sera, two seroconverted to TPPA 1:80+/- after 1-year follow-up. Of 867 CIA-reactive/TRUST-reactive results, 27 (3.1%) were TPPA-nonreactive.

CONCLUSIONS:

The RSA identified more patients with reactive treponemal serology. However, it also yielded an increased likely false-reactive rate compared with the TSA, especially those results with low index values and TRUST-nonreactive serology, were necessary to retest with a second treponemal test. Further testing results with TPPA, VITROS TPA and EuroWB suggested the false-reactive CIA screening results and the likely false-nonreactive TPPA results when the reactive treponemal results screened with RSA were to be identified.

PMID:
30223307
DOI:
10.1111/jdv.15251
[Indexed for MEDLINE]

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