In this article, I have noticed an information, that false positive samples in COVID testing by antigen tests were contaminated by blood:
Liotti FM et al., Performance of a novel diagnostic assay for rapid SARS-CoV-2 antigen detection in nasopharynx samples, Clinical Microbiology and Infection, https://doi.org/10.1016/j.cmi.2020.09.030
Can blood be the cause of the false positivity ?
If yes, what would be the mechanism ? Any particular antigen in the human blood ? Or just the fact, that blood contains more protein than mucus, and causes some unspecific binding to the antibodies ? Are there any similar immunological assays, where blood contamination was a problem ?
Hello!
The transmissibility and severity of COVID-19 infection can be influenced by allelic variants of different human genes and loci ( HLA-B * 4601, FcγRIIA, MBL, TMPRSS2, TNF-α, IL-6, and also blood group A antigen, etc.).
@Alexandr Chernov, thank you, but the topic was different. There are now fast immunological tests to detect coronavirus protein in the nasal mucus. In a general population (not hospital or symptomatic population), they have 1-3% false positivity. I discuss this false positivity.
I have already met a doctor, who has had negative results also from bloody samples. So blood itself is not enough for false positivity.
To what contaminants do you refer? Blood samples could be contaminated with anything but not all contaminants would interfere with blood sample results. I suppose that the blood samples were contaminated with samples positive for COVID-19. Samples other than blood, like mucus, saliva, sputum, swabs, etc. could contaminate intended samples. Please see the link attached for details. https://www.protocols.io/view/cas9-expression-and-purification-protocol-hagb2bw?step=10
@Maurice Ekpenyong , the sample is a mucus from nasopharynx. The blood is a contaminant in the mucus.
One type of rapid diagnostic test (RDT) detects the presence of viral proteins (antigens) expressed by the COVID-19 virus in a sample from the respiratory tract of a person. If the target antigen is present in sufficient concentrations in the sample, it will bind to specific antibodies fixed to a paper strip enclosed in a plastic casing and generate a visually detectable signal, typically within 30 minutes. The antigen(s) detected are expressed only when the virus is actively replicating; therefore, such tests are best used to identify acute or early infection. https://www.who.int/news-room/commentaries/detail/advice-on-the-use-of-point-of-care-immunodiagnostic-tests-for-covid-19#:~:text=One%20type%20of%20rapid%20diagnostic,acute%20or%20early%20infection.
Accurate testing allows identification of people who might need treatment, or who need to isolate themselves to prevent the spread of infection. Failure to detect people with COVID-19 when it is present (a false negative result) may delay treatment and risk further spread of infection to others. Incorrect identification of COVID-19 when it is not present (a false positive result) may lead to unnecessary further testing, treatment, and isolation of the person and close contacts. Correct identification of people who have previously had COVID-19 is important in measuring disease spread, assessing the success of public health interventions (like isolation), and potentially in identifying individuals with immunity (should antibodies in the future be shown to indicate immunity). https://www.cochrane.org/CD013652/INFECTN_what-diagnostic-accuracy-antibody-tests-detection-infection-covid-19-virus
To identify false negative and false positive results, antibody test results are compared in people known to have COVID-19 and known not to have COVID-19. Study participants are classified as to whether they are known or not known to have COVID-19 based on criteria known as the ‘reference standard’. Many studies use samples taken from the nose and throat to identify people with COVID-19. The samples undergo a test called reverse transcriptase polymerase chain reaction (RT-PCR). This testing process can sometimes miss infection (false negative result), but additional tests can identify COVID-19 infection in people with a negative RT-PCR result. These include measuring clinical symptoms, like coughing or high temperature, or ‘imaging’ tests like chest X-rays. People known not to have COVID-19 are sometimes identified from stored blood samples taken before COVID-19 existed, or from patients with respiratory symptoms found to be caused by other diseases. https://www.cochrane.org/CD013652/INFECTN_what-diagnostic-accuracy-antibody-tests-detection-infection-covid-19-virus
Despite being somewhat inaccurate, antigen tests for COVID-19 are fast and easy – and could solve the coronavirus testing problem https://www.google.com/amp/s/theconversation.com/amp/antigen-tests-for-covid-19-are-fast-and-easy-and-could-solve-the-coronavirus-testing-problem-despite-being-somewhat-inaccurate-137977
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