COVID-19

4 Reasons Your Covid-19 Self Test May Give a False Result

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

However, the results obtained with currently available tests are not always perfect barometers for Covid-19 infections. When it comes to precision, rapid tests have always been ahead of PCR tests. While the antigen tests provide results in about 15 minutes, they were only 58% accurate for people who had no symptoms or 72% for those who had symptoms prior to the start of the Omicron variant, according to the report. A Cochrane study of more than 24,000 sample tests.

By comparison, a properly performed PCR test can give lab-approved results with 98% accuracy, according to the same study based on pre-Omicron data. The response time is simply longer and it is supposed to isolate itself during that time.

If you want quick results instead of waiting, here are some things to keep in mind that could affect your test.

Self-assessments have expiration dates

Covid-19 self-test kits are one of the most practical inventions of the pandemic. Several companies offer it without a prescription. While it may be tempting to stock up on these tests at home if you find any, keep in mind that kits expire between several months to a year.

Over-the-counter test kits usually have a label on the box that shows the expiration date and the date of manufacture. The latest date indicates the end of the test’s useful life, which may come earlier than expected; For example, a BinaxNow trial kit purchased at Walgreens in September must expire before the end of January 2022.

Abbott, the maker of the BinaxNow kits, extended their shelf life from six months to one year in May, following review by the Food and Drug Administration (FDA), the U.S. Food and Drug Administration. Similar announcements have been made by companies and expiration dates may be further delayed as the FDA continues to review stability studies.

Meanwhile, users of home test kits should always assume that an expired test result is false.

Hot or cold temperatures can affect components

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

“Do not use rapid tests in very cold weather, as this may decrease their benefits or their effectiveness,” Michael Mina, eMed’s chief scientific officer, said in a conference call with reporters Tuesday. “You have to do this at room temperature for the most part.”

Recommended temperatures for storage and preparation may vary based on testing, so be sure to check the packaging first. The BinaxNow kit, for example, can be stored between 2 and 30 degrees Celsius, but a warning in fine print indicates that all test components are at room temperature before use.

What you ate for lunch can affect a throat swab

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

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

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

Test sites and kits that include mouth swabs advise you to avoid eating, drinking, and smoking for at least 30 minutes before testing. Tips that may be familiar to people living in the UK, where rapid tests generally require a throat swab in addition to a nasal swab.

You should also avoid brushing your teeth or using mouthwash before a throat swab, as good oral hygiene could temporarily remove 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 may not be very effective at detecting Omicron, a variant of the coronavirus that has already shown the ability to evade some of our immune defenses.

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

“We are trying to find the ones that do not 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 Allergies and Diseases. Infectious Diseases in the United States, in an online conversation with the Chamber of Commerce Foundation.

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

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

Original version: Andrea Michelson / Insider

Also read: Omicron variant cases are less likely to be hospitalized, according to two new British studies

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