P1.45 Evaluation of sekure rpr reagent on the sk500 clinical chemistry system. (8th July 2017)

• Record Type: Journal Article
• Authors: Osbak, Kara; Abdellati, S; Tsoumanis, A; Esbroeck, M Van; Crucitti, T; Kenyon, C
• Is Part Of: Sexually transmitted infections. Volume 93(2017)Supplement 2
• Page Start: A61
• Page End: A61
• Publication Date: 2017-07-08
• Subjects: Sexually transmitted diseases -- Periodicals; HIV infections -- Periodicals; 616.951005
• DOI: 10.1136/sextrans-2017-053264.152
• Languages: English
• ISSNs: 1368-4973

Abstract

Abstract : Introduction: An automated and accurate laboratory assay would be of considerable utility to the diagnosis of syphilis and treatment follow-up. We compared the Sekure RPR (Rapid Plasma Reagin) test performed on the SK500 Clinical Chemistry System to RPR card test results. Methods: Serum samples were collected in the context of a 2 year observational cohort study of syphilis infected patients and controls. Syphilis was diagnosed using non-treponemal and treponemal testing. Sera collected at the time of diagnosis (M0) and at 3, 6, 9 and 12 months post-treatment were tested by a Macro-Vue RPR card test (RPR-C) (Becton Dickinson) and a Sekure RPR test (RPR-S) (Sekisui Diagnostics). RPR-S results are expressed in RPR units (R.U.), whereby 1 R.U. equals a 1-fold change in RPR-C titre. The agreement, linearity and reportable ranges were determined using RPR-C results as the gold standard. Linear regression was used to assess correlations from before and after implementation of an extra dilution step for samples with a strong suspicion of prozone effect. Results: In total, 451 samples from 150 participants were tested, including 120 new syphilis cases and 30 controls. All 30 controls tested negative. Initially there was a weak correlation between RPR-C and RPR-S values (r=0.15). Further analyses identified 72 RPR-S samples with a strong suspicion of prozone effect. We therefore included an extra dilution step (10x) and retested 60/72 samples; values within the expected range were obtained for 58 of them. After implementing the extra dilution step the correlation was moderate (r=0.61), increasing further to r=0.91 for samples with RPR-C titres≤128. Of the 92 samples that tested RPR-C positive and RPR-S negative, 8 were from M0 (RPR-C: 1–4), which would have led to missed diagnoses. Conclusion: A reasonable correlation was found between the tested methods for mid-range RPR-C results (titre ≤128). However, prozone may occur in samples with high antibody concentrations. More investigation is required to elucidate the false negative RPR-S results.