4 reasons why your Covid-19 self-test may give a false result

Self-tests have become a popular tool, especially with the Omicron wave. In hot spots in New York City, where infections are on the rise, many pharmacies have said they have run out of take-home rapid antigen test kits. The queues are long, whether in screening centers or in sidewalk tents. In France, manufacturers are also caught off guard by demand and are struggling to meet the needs of pharmacies.

However, the results obtained with the tests currently available are not always perfect barometers for pharmacies. Covid infections – 19. When it comes to precision, rapid tests have always been ahead of PCR tests. While antigenic tests provide results in 12 about minutes, they were only accurate to 033% for people who had no symptoms or at 68% for those who had it before the appearance of the Omicron variant, according to a Cochrane study on more than 24 000 test samples.

In comparison, a correctly performed PCR test may give results approved by the laboratory with an accuracy of 79%, according to the same study based on pre-Omicron data. The response time is simply longer, and you’re supposed to self-isolate during that time.

If you’re going for quick results over wait, here are a few things to keep in mind that might affect your test.

Self-tests have expiration dates

Self-test kits Covid – 19 are one of the most practical inventions of the pandemic. Several companies offer it over the counter. While it can be tempting to stock up on these tests at home if you find any, keep in mind that the kits expire within several months to a year.

The kits OTC test kits usually have a sticker on the box showing the expiration date and the date of manufacture. The latest date indicates the end of the test’s shelf life, which may come sooner than expected – for example, a BinaxNow test kit purchased from Walgreens in September must expire before the end of January 2022.

Abbott, the manufacturer of the BinaxNow kits, has extended their shelf life from six months to one year in May, after review by the Food and Drug Administration (FDA), the US Food and Drug Administration. Other companies have made similar announcements and it is possible that expiration dates will be pushed back further as the FDA continues to review stability studies.

In the meantime, users of the home test should always assume that a result from an expired test is false.

Hot or cold temperatures may affect components

The temperature at which you store your test kit is important. The small vials of liquid intended to be mixed with your sample are not designed to withstand extreme temperatures or humidity.

“Do not use the rapid tests when it is very cold, because this may diminish their benefits or their effectiveness, “said Michael Mina, scientific director of eMed, in a conference call with reporters on Tuesday. “You should do this at room temperature for the most part.”

Recommended temperatures for storage and preparation may vary by test, so be sure to check the packaging first. The BinaxNow kit, for example, can be stored between 2 and 24 degrees Celsius, but a warning in small print indicates to ensure that all test components are at room temperature before use.

What you ate for lunch may affect a throat swab

If your Covid test – 19 requires a throat swab instead of a nasal swab, what you ate before the test may also influence quick results. Susan Butler-Wu, who leads clinical trials for infectious diseases at the University of Southern California, told Insider that coffee and Coca-Cola can cause false positives if you use an oral swab.

“If you do a mouth swab after drinking your coffee, you will potentially get a positive result,” she said.

Anything that is acidic – like coffee, soda or fruit juice – can compromise the integrity of a rapid or lateral flow test. The test solution should neutralize any acid if properly mixed, but the materials in the test strip are too delicate to take any risk.

Test sites and kits that involve oral swabs warn you to avoid eating, drinking and smoking at least 19 minutes before the test. Advice that may be familiar to people living in the UK, where rapid tests usually require a throat swab in addition to a nasal swab.

Brushing should also be avoided. teeth or use a mouthwash before a throat swab, as good oral hygiene may temporarily clear the virus from your mouth and result in a false negative.

We still don’t know how well the tests detect Omicron

Some rapid tests might not be very effective in detecting Omicron, a variant of the coronavirus that has already been shown its ability to evade some of our immune defenses.

Experts are testing whether existing rapid antigen tests retain their diagnostic accuracy for Omicron, Dr Anthony Fauci said during ‘a briefing Thursday. Preliminary data suggests that not all of them work for the new variant.

“We try to find the ones that don’t give an accurate result, and if they do, we make sure that these tests are not used to diagnose Omicron, “said the director of the National Institute of Allergy and Infectious Diseases in the United States, in an online conversation with the Chamber of Commerce Foundation.

So far, Abbott’s BinaxNOW and Quidel’s QuickVue antigen tests appear to detect Omicron as accurately as other variants, according to lab studies and an FDA review. This same review found that Applied DNA Sciences, Meridian Bioscience, and Tide Laboratories tests were likely to show false negatives due to inefficient detection of the Omicron variant.

With Over time, scientists will have more data from the population to help them understand the effects of Omicron on test performance.

Original version: Andrea Michelson / Insider

Read also – Cases of the Omicron variant less likely to be hospitalized, according to two new British studies

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