Assessment of a fully automated RPR assay (Mediace RPR) for serological diagnosis and follow-up of syphilis: a retrospective study

Abstract

Objectives: This study assessed the Mediace RPR assay, an automated RPR (aRPR), for syphilis diagnosis and serological follow-up.

Methods: Serums from patients positively screened for syphilis between January 2017 and December 2019 were retrospectively selected. A focus was performed on patients with a serological follow-up after treatment and/or a reinfection. Serums were tested by both manual (mRPR) and aRPR tests. Categorical and Quantitative Agreements (CA and QA), and serological follow-up conclusions were analyzed.

Results: 236 serums from 85 patients (99% of male, 66% of HIV-infected) were included. The overall QA was 54.2%. CA was low (79.7%) especially for samples with low RPR titers. No prozone effect was observed. Serological follow-up after treatment led to similar conclusions, although aRPR titers often decreased faster. Over 26 episodes of reinfection, 4 (15.4%) were misdiagnosed with the aRPR.

Conclusions: While the Mediace aRPR presents the advantages of an automated test, its poor sensitivity in low titers may limit its use.

Keywords: Automated non-treponemal test; Rapid plasma reagin; Syphilis; Syphilis follow-up; Treponema pallidum.