Evaluation of an automated quantitative latex immunoturbidimetric non-treponemal assay for diagnosis and follow-up of syphilis

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Abstract

PURPOSE: We evaluated the Sekure rapid plasma reagin (RPR-S) (Sekisui Diagnostics) automated quantitative latex immunoturbidimetric assay performed on the SK500 clinical chemistry system for clinical appropriateness.

METHODOLOGY: Syphilis-infected individuals and controls were recruited into a prospective cohort study conducted at a sexually transmitted infection clinic in Antwerp, Belgium. Sera collected at diagnosis (baseline) and at 3, 6, 9 and 12 months post-treatment were tested with RPR-S and Macro-Vue RPR card (RPR-C) (Becton Dickinson) assays; RPR-C was considered the reference test. IgG/IgM enzyme immunoassay and Treponema pallidum polA serum PCR results were consulted by discordancy at baseline. Categorical analyses were performed and correlations were assessed with (non)-linear regression. Post-treatment longitudinal serological evolution was evaluated.

RESULTS: A total of 463 samples from 120 new syphilis cases from a variety of clinical stages and 30 syphilis-negative controls were tested. Initially, there was a weak correlation between quantitative RPR-C/S (r=0.15). In 70 samples there was a strong suspicion of hook effect. Of these, 57/70 sera were retested with an extra dilution step, resulting in an average 12-fold increase in quantitative RPR-S results. After the extra dilution, the overall qualitative RPR-C/S agreement was 78.89 %, (κ-coefficient: 0.484). Of the 92 discordant samples, 9 were from the baseline visit (RPR-C titre: 1-8), which could have led to possible missed diagnoses using the RPR-S.

CONCLUSIONS: The sensitivity and accuracy of the RPR-S test requires improvement before it can be used to diagnose syphilis and evaluate treatment efficacy in clinical practice.

Original languageEnglish
JournalJournal of Medical Microbiology
Volume66
Issue number8
Pages (from-to)1130-1139
Number of pages10
ISSN0022-2615
DOIs
Publication statusPublished - 2017

Keywords

  • diagnostics
  • Treponema pallidum
  • syphilis
  • non-treponemal test
  • hook effect
  • sexually transmitted infections
  • screening
  • HUMAN-IMMUNODEFICIENCY-VIRUS
  • PROZONE PHENOMENON
  • RPR TEST
  • INFECTION
  • PALLIDUM
  • TESTS
  • GUIDELINES
  • CHEMISTRY
  • AGREEMENT
  • SEROLOGY

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