Absence of risk factors for false-positive test results in blood donors with a reactive test result in an automated treponemal test (PK-TP) for syphilis

BACKGROUND: Screening and confirmatory serologic tests for syphilis are kno wn to generate false-positive results in low-risk populations, which includ e blood donors. This study assessed whether conditions previously reported to cause biological false-positive (BFP) test results for syphilis are rele vant to contemporary syphilis testing of blood donors and the extent to whi ch seropositive donors report a history of syphilis. STUDY DESIGN: AND METHODS: A history of conditions reported to be associate d with BFP syphilis tests or a history of syphilis infection was assessed b y a case-control study of donors with reactive and nonreactive automated tr eponemal test results, using an anonymous mail survey. Analysis of cases wa s stratified by fluorescent treponemal antibody absorption (FTA-ABS) result . RESULTS: Adjusted ORs (95% Cls) for reported BFP-associated conditions were 1.3 (0.3-2.1) for FTA-ABS-positive cases and 0.8 (0.3-1.9) for FTA-ABS-neg ative cases. Among responding blood donors, syphilis history was reported i n 78 (51%) of 153 FTA-ABS-positive cases, 0 of 142 FTA-ABS-negative cases. and 3 (0.4%) of 716 automated treponemal test (PK-TP)-negative controls. CONCLUSION: Approximately half of donors with FTA-ABS-positive test results reported a syphilis history. There was no difference between reported BFP conditions for FTA-ABS-positive or FTA-ABS-negative cases and controls. Thi s information may be useful when providing donors with better predonation o r post-test counseling information about syphilis testing.