Evaluation of positive and false‐positive results in syphilis screening of blood donors in Rio de Janeiro, Brazil

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Syphilis is a disease that has been studied for centuries, and serological tests represent an important tool for diagnosis. Since the discovery of the first syphilis serological test 110 years ago (Bialynicki‐Birula, 2008), many testing options with varied methodologies have become available. However, no test alone can be considered definitive.
Treponemal tests such as enzyme‐linked immunosorbent assay (ELISA) and chemiluminescent immunoassay (CLIA) have been widely used as alternatives to the traditional nontreponemal tests, i.e. the Venereal Disease Research Laboratory (VDRL) and Rapid Plasma Reagin (RPR), due to the formers' advantages, such as objectivity and the possibility of automation. However, the treponemal assays used for syphilis screening, in contrast to the confirmatory testing of the initial nontreponemal positive results, have a low positive predictive value for infectious syphilis among low‐prevalence populations. Thus, these methods require reflex testing and possibly a second treponemal test with an alternative platform for confirmation (Young, 2000). This reverse algorithm has resulted in increased reactivity rates for syphilis (Mishra et al., 2011), and false‐positive cases represent a significant proportion of the results (van Dommelen et al., 2015). Unconfirmed treponemal screening tests require close monitoring. This is a clinical dilemma for follow‐up and treatment and can represent a loss of healthy donors and the increased disposal of blood products in blood banks.
The use of high‐sensitivity testing in blood donor screening is essential to ensure transfusion safety. However, it is also important that the tests maintain high specificity to minimise the possible losses of healthy donors, particularly in areas with few donors.
This study analysed the positive and false‐positive result profiles among blood donors from the Instituto Nacional de Câncer José Alencar Gomes da Silva (INCA), Rio de Janeiro, Brazil, by comparing the use of a nontreponemal test (VDRL) with a treponemal test (CLIA). Additionally, we investigated possible factors associated with positive and false‐positive results of the recently introduced test.

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