On January 7, 2022, the Journal of the American Medical Association – JAMA was published, the largest study to date to determine the percentage of false-negative antigen rapid test results. These tests are widely used to scan asymptomatic individuals who have come in contact with SARS-CoV-2 and may be infected.
The study was conducted in Canada, from January to October 2021, and assessed the fidelity of nearly one million rapid antigen tests in over 500 different regions of the country. The Professors of EKPA Ourania Tsitsiloni, Evangelos Terpos, Ioannis Trougakos and Thanos Dimopoulos (Rector of EKPA) analyze the results of the study.
Of the approximately one million rapid tests evaluated, 0.15% were positive, almost all of which were confirmed to be true positive by molecular RT-PCR.
The percentage of false positive tests was very low, only 0.05% (ie 5 false positives per 10,000 rapid tests).
An important element of the study was that most of the false positive tests were done with a specific batch of rapid tests from a well-known company that manufactures and markets such tests. In fact, according to the results of the study, over 50% of the false positive rapid tests were due to problems in the production of rapid tests. Therefore, the quality control of rapid tests by the companies should be intensified, before they are put on the market.
A second parameter concerns the time of the rapid test. It is very likely that many false positives were the result of a test either too early or too late during the infection.
The third important parameter concerns the way the sample is taken and the rapid test is performed. If the nasopharyngeal specimen is not taken correctly or the test specification on the package is not followed, it is very likely that the result will be false positive.
At this point, there is a recent and intense concern in the scientific community, as reported in The Washington Post on January 6, 2022 (https://www.washingtonpost.com/wellness/2022/01/06/adding-throat- swab-covid-test), which involves taking a sample not only from the nasopharynx (nose) but also from the oropharynx (deep in the mouth). Distinguished American epidemiologists believe that in view of the spread of the “micron” mutation, which infects and multiplies 70 times faster than the “delta” mutation and the Wuhan virus, the probability of detecting the “micron” in an oral sample is much higher. In fact, in Canada and the United Kingdom, the modern use of a nasal and oral smear in rapid antigen tests is already proposed. However, the US FDA statement is the exact opposite: circulating rapid antigen tests have not been evaluated and validated in oral coatings, and any derogation from the enclosed rapid test guidelines is currently not recommended. In addition, the FDA focuses its concern on two points: (1) the dangers of taking a mouthwash by non-health professionals, stressing that this procedure can cause serious injury to the test subject when he or she tries to take it alone, and (2) in the possibility of false results, knowing that the oral cavity is particularly rich in microorganisms (eg bacteria, viruses) that can alter the result of the rapid antigen test.
In conclusion, the test with antigen rapid test is reliable and at a rate of 99.95% gives the correct result, provided that it has been done according to the manufacturer’s instructions and at the right time. For the low probability of a false positive result due to a mistake of the production company or a wrong sampling, it is recommended to repeat the test after 2 days using an antigenic rapid test of another company which, again, must be performed according to the instructions of the production and distribution company .
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