Commercial Treponemal Assays Compared for Syphilis Detection

Treponemal tests for detecting syphilis should be sufficiently sensitive and specific, especially when used as the first-line method in reverse-algorithm testing.

Syphilis is a sexually transmitted disease caused by the bacterium Treponema pallidum subspecies pallidum, and the disease can mimic a variety of conditions in its clinical presentation and therefore, laboratory analysis in combination with clinical presentation plays an important role in the diagnosis of syphilis.

Microbiologists at the Star-MDC, Laboratory for Medical Microbiology (Rotterdam, The Netherlands) tested a total of 1,251 patient samples for the presence of T. pallidum antibodies. Fresh samples were taken from 500 pregnant women in the course of regular obstetric care, and 701 samples were drawn from at-risk individuals suspicious for syphilis. Another 50 samples were remnant samples that had been stored at −25 °C from known positives previously diagnosed and treated for syphilis.

The scientists tested all samples in duplicate using each of three treponemal assays: the ADVIA Centaur Syphilis assay, the IMMULITE 2000 Syphilis Screen (Siemens; Erlangen, Germany), and the Bioelisa Syphilis 3.0 assay (Biokit; Lliçà d'Amunt, Spain). Reactive samples—those reactive according to at least two of the three treponemal methods—were further evaluated using Euroline Western blot immunoglobulins IgG and IgM (Medizinische Labordiagnostika; Lübeck, Germany), and Venereal Disease Research Laboratory (VDRL) testing.

Overall, positive and negative agreement was 100% between the Centaur and IMMULITE assays. The overall agreement was 99.92% between either of the Siemens assays and the Biokit assay; positive agreement was 99%, and negative agreement was 100%. The investigators found 11/1,251 (0.88%) of the samples were interpreted as positive/reactive based on the combined positive results by the ADVIA Centaur, IMMULITE 2000, and bioelisa assays; a positive Euroline anti-Treponema pallidum IgM blot; and a VDRL result of equal to or greater than 1:8. In this study, no false-reactive samples were identified using this method.

The authors concluded that the greater than 99% agreement of the Siemens assays with the Biokit assay indicates that sensitivity and specificity are likely comparable. They therefore feel that the use of the three treponemal assays in this study constitutes sufficient evidence for confirmation of reactivity. The study was published on June 10, 2014, in the journal Clinica Chimica Acta.

Related Links:
Star-MDC
Siemens Healthcare
Biokit