Handle rapid antigen tests for Covid-19 with care, especially when they are used on asymptomatic people: depending on the context in which they are used, they can in fact miss an important slice of positive and potentially infectious cases. This is the appeal that comes from a study published in the British Medical Journal and conducted by the universities of Birmingham and Oxford and by Imperial College London.
The study, the researchers clarify, does not question the usefulness of this type of exams. Rapid tests, in technical jargon ‘lateral flow tests’, “are an important tool for controlling the pandemic – it reads -, however, claims that lateral flow tests can identify’ the vast majority of people who are infectious. ‘are likely overrated and risk providing false reassurance to those who take a test to try to rule out infection.’
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The study assessed the reliability of rapid tests in three settings: British Health Service Diagnostic Centers for Symptomatic People, asymptomatic screening centers in Liverpool, and a University of Birmingham screening of students prior to their return to home at the end of 2020. The comparison between the results of the rapid examination and the in-depth molecular test showed that the rapid tests had missed 20% of the positives when carried out on the symptomatic, 29% in the Liverpool program and the 81% in that of the University of Birmingham. Not only that: among the positives escaped the test, respectively 38%, 47% and 90% were in their vote responsible for further infections.
The researchers warn that these data could overestimate the phenomenon and “must therefore be taken as illustrative and not exact.” They also refer to a specific test that is particularly popular in the UK.
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“Doctors and policy makers need to be aware of the limitations” of rapid tests, the researchers add. It would also be advisable “that the tests are not used in situations where the consequences of a false negative result are particularly serious”, they conclude.
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