Urea-mediated dissociation alleviate the false-positive Treponema pallidum-specific antibodies detected by ELISA

Abstract

The serological detection of antibodies to Treponema pallidum is essential to the diagnosis of syphilis. However, for the presence of cross-reaction, the specific antibody tests [e.g., enzyme-linked immunosorbent assay (ELISA)] always have false-positive results. In this study, we derived and validated the dissociation of urea in an attempt to alleviate the situation of false-positive antibodies to T . pallidum detected by ELISA. Six serum samples that were false-positive antibodies to T . pallidum detected by ELISA, and 16 control serum samples (8 sera positive for both specific IgG and IgM, and 8 IgG-positive and IgM-negative sera) were collected to select the appropriate dissociated concentration and time of urea. Our goal was to establish improved an ELISA method based on the original detection system of ELISA. The sensitivity of the improved ELISA was evaluated by 275 serum samples with class IgM-positive antibodies to T . pallidum . At 6 mol/L with 10 minutes dissociation of urea, 6 samples with false-positive antibodies to T . pallidum were converted to negative, and compared with true-positive antibodies to T . pallidum . The sensitivity of the improved ELISA was 100% by detecting the class IgM-positive antibodies to T . pallidum in sera of patients with syphilis. Considering the importance at the diagnosis of syphilis, antibodies to T . pallidum in serum samples should be retested by the improved ELISA method to avoid false-positive results.

False-positive results of SARS-CoV-2 IgM/IgG antibody tests in sera stored before the 2020 pandemic in Italy

“…The urea treatment was performed using sera from the rRT-PCR-positive controls, as well as the samples that had tested positive for IgM and/or IgG in either test. For the rapid test, the urea dissociation concentration (6 mol/L) and duration (25 min) were in line with previous studies ( Wang et al, 2019 , Wang et al, 2020 ); for ELISA, two different concentrations were tested in different wells: 4 mol/L, previously reported to be the best concentration ( Wang et al, 2020 ), and 6 mol/L. Results were expressed as the Affinity Index (AI) and interpreted according to the threshold values calculation method described by Wang et al (2020) .…”

“…The urea dissociation test, recently proposed by Wang et al, is based on the principle that urea dissociates the antigen-antibody reactions. The test has been used to evaluate the affinity of IgM and IgG for different pathogens ( Wang et al, 2019 , Wang et al, 2020 ). The urea treatment was performed using sera from the rRT-PCR-positive controls, as well as the samples that had tested positive for IgM and/or IgG in either test.…”

Impact of the COVID-19 outbreak and the serum prevalence of SARS-CoV-2 antibodies in patients with inflammatory bowel disease treated with biologic drugs

“…Both position papers were in favor of continuing administering biologic therapies to IBD patients as there is no evidence of increased risk associated with these drugs. Danese et al suggested the IBD Units may be reorganized in a way that the safety of IBD patients is guaranteed during the COVID-19 pandemic while they continue receiving all the necessary therapies for IBD [20] . In particular, the authors recommend establishing checkpoints at the hospital entrances to screen people with suspected upper respiratory symptoms, to allow entry only to patients without accompanying people, to investigate close contacts with confirmed or suspected COVID-19 infected patients, to respect social distancing during visits and therapy administration, and to use protective personal equipment (surgical masks and gloves) [20] .…”

A method to alleviate false-positive results of the Elecsys HIV combi PT assay

“…Urea is a type of dissociating agent that, functions to dissolve and denature protein. Previous studies in our laboratory have found that urea-mediated dissociation alleviates the false-positive Treponema pallidum -specific antibodies detected by ELISA 19 . However, whether urea-mediated dissociation can reduce the false-positive rate of the Elecsys HIV combi PT assay has not been studied.…”