Absence of risk factors for false‐positive test results inblood donors with a reactive test result inan automated treponemal test (PK‐TP) for syphilis

Abstract
BACKGROUND: Screening and confirmatory serologic tests for syphilis are known to generate false‐positive results in low‐risk populations, which include blood donors. This study assessed whether conditions previously reported to cause biological false‐positive (BFP) test results for syphilis are relevant to contemporary syphilis testing of blood donors and the extent to which seropositive donors report a history of syphilis.STUDY DESIGN AND METHODS: A history of conditions reported to be associated with BFP syphilis tests or a history of syphilis infection was assessed by a case‐control study of donors with reactive and nonreactive automated treponemal test results, using an anonymous mail survey. Analysis of cases was stratified by fluorescent treponemal antibody absorption (FTA‐ABS) result.RESULTS: Adjusted ORs (95% CIs) for reported BFP‐associated conditions were 1.3 (0.8‐2.1) for FTA‐ABS‐positive cases and 0.8 (0.3‐1.9) for FTA‐ABS‐negative cases. Among responding blood donors, syphilis history was reported in 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. This information may be useful when providing donors with better predonation or post‐test counseling information about syphilis testing.