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 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.


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.


CONCLUSIONS
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.
Orton
S L
SL
American Red Cross Holland Laboratory, Rockville, Maryland, USA.
Dodd
R Y
RY
Williams
A E
AE
D000293:Adolescent; D000328:Adult; D001782:Blood Donors; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013587:Syphilis / Q000175:diagnosis* / Q000517:prevention & control* / Q000635:transmission; D065227:Transfusion Reaction; D014209:Treponema Immobilization Test