RT Journal Article SR Electronic T1 Development of a novel magnetic particle-based agglutination immunoassay for anticardiolipin antibody detection in syphilis JF Sexually Transmitted Infections JO Sex Transm Infect FD BMJ Publishing Group Ltd SP 411 OP 416 DO 10.1136/sextrans-2020-054437 VO 96 IS 6 A1 Mayur R Shukla A1 John W Deutsch A1 Lara E Pereira A1 Ellen N Kersh A1 Yetunde F Fakile YR 2020 UL http://sti.bmj.com/content/96/6/411.abstract AB Objectives Serological tests of non-treponemal and treponemal types are the most frequently used for syphilis diagnosis. Treponemal tests are available in wide variety of assay formats; however, limited advances have been made for the improvement of conventional non-treponemal tests. The objective of this work was to develop a novel non-treponemal magnetic particle-based agglutination assay (NT-MAA) and evaluate its feasibility for syphilis testing.Methods Cardiolipin was modified and coupled to magnetic microbeads. Serum diluted in phosphate-buffered saline was mixed with cardiolipin-coupled beads and incubated in a round bottom microplate for 90–120 min followed by visual inspection. A panel of reported syphilis (n=127) and non-reactive (n=244) specimens was prepared to evaluate the NT-MAA performance in comparison to conventional rapid plasma reagin (RPR). Treponema pallidum particle agglutination (TP-PA) assay and enzyme immunoassay (EIA) were included. Analytical sensitivity and reproducibility of NT-MAA were also determined.Results The non-treponemal NT-MAA and RPR showed sensitivity of 90.6% and 88.2% and specificity of 96.7% and 100%, respectively. The treponemal TP-PA and EIA yielded sensitivity of 100% and 99.2%, respectively, and 100% specificity by both assays. The per cent agreement between NT-MAA and RPR was 97% (kappa=0.931, 95% CI 0.891 to 0.971). Analytical sensitivity determined with IgM anticardiolipin antibody (ACA) was 2.6 µg/mL for both NT-MAA and RPR, while IgG ACA yielded 0.9 µg/mL and 1.7 µg/mL for NT-MAA and RPR, respectively. Qualitative results of intra-assay and interassay reproducibility revealed 100% consistency for NT-MAA.Conclusion Preliminary evaluation of the novel NT-MAA validated proof of concept using laboratory-characterised syphilis sera and demonstrated performance comparable to RPR. Further validation of NT-MAA using additional specimens with better clinical staging may broaden the scope of developed test for syphilis diagnosis.