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False-positive test results: prevalence, time trends, and factors associated with false-positive serological markers
Lucas Kallas-Silva1, Leandro Dinalli Dos Santos2, Valeria de Freitas Dutra2
1Faculdade Israelita de Ciencias da Saude Albert Einstein, Hospital Israelita Albert Einstein, São Paulo, Brazil.
Background And Objectives:
False-positive serological results in blood donation screening may arise from antibody cross-reactivity, limitations in assay specificity, or low-level reactivity during early-stage infections, ultimately leading to donor deferral and the discard of viable blood units. This study evaluated the prevalence, time trends, and demographic factors associated with false-positive serologic screening results for transfusion-transmissible infections in a Brazilian blood center.
Materials And Methods:
A cross-sectional study was conducted including all blood donations collected between 2013 and 2022 at a private blood center in São Paulo, Brazil. Donations were screened with serologic tests for syphilis, human immunodeficiency virus, hepatitis B virus, and hepatitis C virus. Reactive samples underwent confirmatory testing, where a false-positive result was defined as an initially reactive screening assay followed by a nonreactive confirmatory test. Associations between demographic variables and false-positive or true-positive results compared to true negative results were analyzed using multivariable Poisson regression.
Results:
A total of 129,166 donors were included. Most donors (98.7%) had nonreactive results for all serologic tests. Reactive screening results were observed in 0.5% of donations for both syphilis and hepatitis B virus, 0.2% for hepatitis C virus, and 0.1% for human immunodeficiency virus. False positivity occurred more frequently for human immunodeficiency virus (92.0%) and hepatitis C virus (72.7%). Older age, lower education levels, and first-time donation were associated with false-positive results, whereas male sex, non-white race/skin color, lower education levels, and being single or divorced were associated with true-positive status.
Conclusion:
False-positive results were more frequent among first-time and less-educated donors. This study found no consistent overlap between demographic factors associated with false positivity and true positivity. This suggests that false positivity mainly occurs by chance or from antibody cross-reactivity.
