There are many cases of patients with Covid-19 who, despite the presence of symptoms, the first results of the rapid test were negative. It even took several days for a double red line to appear on their test.

For their part, experts say rapid detection tests continue to be a useful tool in containing the spread of the virus. COVID-19-19, but they are by no means infallible.

Professors of laboratory medicine explain the reasons why rapid tests still show false negative results, especially during the first symptoms.

Why a rapid test shows a false negative result

Explanation #1 – Low Viral Load

The most likely reason why a rapid test may give a false negative result is that the viral load is not yet high.

“These specific tests are just not that sensitive,” said Dr. Sheldon Campbell, professor of laboratory medicine at Yale School of Medicine, noting that this applies to all rapid detection tests.

“Rapid tests essentially confirm that you can transmit the virus, regardless of when you were infected,” said Dr. Paul Drain, assistant professor of global health at the University of Washington, stressing that in the case of Covid-19, what really matters is prevent its spread.

In addition, to qualify for emergency use approval from the Food and Drug Administration, companies must demonstrate at least 80% accuracy on rapid tests.

Another large study showed that rapid tests correctly detect infection. FROMovoid-19 in 73% (and if the person has symptoms). If a person has no symptoms, the accuracy drops to 55%.

Explanation #2 – Errors in using tests

Another possible explanation for a false negative test result is that you didn’t follow the instructions exactly.

Experts recommend always blowing your nose before taking a test. This is because the rapid test detects the virus in the cells inside the nose and not in the mucus.

Tests do not lose their accuracy over time

In any case, the appearance of a new variant does not seem to affect accuracy. Several studies have shown that rapid detection tests were as successful with the first Omicron variant as they were with other strains.

“The tests are designed to detect the nucleoprotein, and because the nucleoprotein has not mutated, we can be confident that the tests will still work as well as they have in the past,” said Hafer, assistant professor of molecular medicine at the Massachusetts Chan School of Medicine School of Medicine. university.

For its part, the FDA recommends that citizens undergo a so-called “serial screening” if they develop symptoms. “If you think you have contracted the coronavirus, but the test is negative, repeat the test after 48 hours. If you still have a negative result, do another test within the next two days,” the FDA said in a statement.

Source: Seattletimes