PT - JOURNAL ARTICLE AU - Kara Osbak AU - S Abdellati AU - A Tsoumanis AU - M Van Esbroeck AU - T Crucitti AU - C Kenyon TI - P1.45 Evaluation of sekure rpr reagent on the sk500 clinical chemistry system AID - 10.1136/sextrans-2017-053264.152 DP - 2017 Jul 01 TA - Sexually Transmitted Infections PG - A61--A61 VI - 93 IP - Suppl 2 4099 - http://sti.bmj.com/content/93/Suppl_2/A61.1.short 4100 - http://sti.bmj.com/content/93/Suppl_2/A61.1.full SO - Sex Transm Infect2017 Jul 01; 93 AB - 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.