Syphilis testing algorithms: A review

The evaluation of the reverse algorithm for syphilis screening in blood donors

Background: In Turkey, prior to transfusion and apheresis, it is mandatory to screen blood for HBsAg, anti-HCV, anti-HIV 1/2, and syphilis. In recent years, efforts have been made to create effective diagnostic algorithms for screening, and as a screening strategy, many countries have switched from traditional algorithms to reverse algorithms. This study was carried out to evaluate the results we obtained after changing to chemiluminescence immunoassay (CLIA) based reverse algorithm, which is more sensitive and specific than the traditional algorithm and VDRL test we currently use for syphilis screening.

Methods: The screening algorithm was initiated with the treponemal CLIA method. The reactive samples were tested using a nontreponemal test VDRL and a second treponemal test TPHA. In the descriptive analyses, the averages, numbers, and percentage distributions were calculated. The group comparisons were undertaken with the chi-square test, accepting p < 0.05 as statistically significant.

Results: Of the 5,053 samples that were tested with CLIA syphilis TPA assay 5,043 were negative (99.802%) and 10 were positive reactive (0.198%), and the difference between the two was statistically significant (p < 0.001). Ten samples that were recurrently reactive were analyzed by VDRL and TPHA tests simultaneously. VDRL was negative in all 10 samples, whereas TPHA was negative in one sample, but positive in nine samples at a titer of ≥1/160.

Conclusion: Based on the results of this study, we decided to use the CLIA method and reverse algorithm instead of using the traditional algorithm and VDRL as the initial screening method.

Evaluation of a Multiplex Fully Automated Treponemal and Nontreponemal (Rapid Plasma Reagin) Assay

OBJECTIVES

In June 2017, Bio-Rad Laboratories received US Food and Drug Administration clearance for its BioPlex 2200 Syphilis Total & RPR (rapid plasma reagin) assay. It is the first fully automated treponemal/nontreponemal multiplex flow immunoassay, simultaneously detecting Treponema pallidum and reagin antibodies and an RPR titer. We compared the performance of the BioPlex Syphilis Total & RPR assay with the LIAISON Treponema Assay and the manual BD Macro-Vue RPR 18-mm Circle Test.

METHODS

In total, 314 serum specimens were tested for treponemal immunoglobulin G/immunoglobulin M and RPR with the LIAISON Treponema Assay, the BioPlex 2200 Syphilis Total & RPR assay, and the manual BD Macro-Vue RPR card test. All discordant results were further tested with the T pallidum particle agglutination assay from Fujirebio Diagnostics.

RESULTS

The overall percent agreement for the BioPlex assay for treponemal antibodies with the LIAISON Treponema Assay was 96.1%. Sensitivity and specificity for the BioPlex RPR assay were 90.5% and 97.2%, respectively (the manual RPR assay was considered the gold standard).

CONCLUSIONS

The BioPlex 2200 Syphilis Total & RPR assay performance was comparable to the LIAISON Treponema Assay and the manual RPR test. Compared with the manual RPR, the automation of RPR testing offered labor savings, objective result reporting, and improved workflow.