Improved efficiency using sequential automated immunoassays for syphilis screening in blood donors

Using sequential immunoassays for the screening of blood donors is well described for viral serology testing but not for the screening of syphilis. In this study, we report the evaluation results and 2-year sequential testing data using two highly sensitive automated serology assays, the Alinity s Syphilis chemiluminescent immunoassay for screening, with all repeatedly reactive samples then tested on the Elecsys Syphilis electrochemiluminescence immunoassay. We screened 1, 767, 782 blood donor samples between 7 July 2021 and 6 July 2023 and found the Alinity false-positive rate to be low at 0.08% (1, 456/1, 767, 782). The common false-positive rate between the two assays was also low (3.83%, 58/1, 514). Concordantly reactive samples were further tested using a Treponema pallidum particle agglutination test, a rapid plasma reagin test, and a fluorescent treponemal antibody absorption test. There were 262/1, 376 concordantly reactive Alinity and Elecsys blood donor samples with reactivity on one or more of the confirmatory tests. A total of 26/1, 376 donors had a current syphilis infection, 152/1, 376 reported a past history of syphilis and had been treated, and 84/1, 376 did not report a past history of syphilis. We suggest that future studies could explore the use of sequential immunoassays to aid in the serodiagnosis for syphilis.