Comparison of conventional immunochromatographic assay with new automated-Treponema pallidum hemagglutination assay for screening of syphilis in blood donors

Introduction: Serological tests for syphilis contributed greatly to the detection of Treponema pallidum infection in blood donors and especially in those who were missed during the medical selection. Although several different treponemal assays have been evaluated in India, the debate that which treponemal test-formats would be suitable for a particular blood transfusion service is far from settled. Aims and Objectives: The study was undertaken with an objective of comparing conventional immunochromatographic assay (ICA) with new automated T. pallidum hemagglutination assay (a-TPHA) in over 10,000 consecutive blood donor samples with fluorescent treponemal antibody-absorption assay (FTA-Abs) as the gold standard to resolve the discordant samples. Materials and Methods: The study was conducted in the Department of Transfusion Medicine in a large tertiary care hospital in India. Consecutive blood donors from July 2014 to January 2015 were evaluated simultaneously for antitreponemal antibodies by solid-phase ICA (SD BIOLINE Syphilis 3.0, Alere Medical Pvt. Ltd., USA), a-TPHA (Immucor Diagnostics, USA) and FTA-Abs (Biocientifica SA, FTA-Abs, Argentina). Performances of both the assays were evaluated using statistical tools. Results: A total of 10,129 donor samples were evaluated. A total of 113 (1.1%) donor samples were reactive for syphilis; either on ICA or a-TPHA or both. Ninety-one of these 113 reactive samples were reactive on FTA-Abs, giving seroprevalance of syphilis as 0.9%. a-TPHA was superior to ICA in terms of sensitivity, specificity, positive predictive value, negative predictive value, and Youden's index. Conclusion: The new “a-TPHA” is a superior assay to ICA as the screening assay for syphilis in blood donors.