4 Reasons Your Rapid COVID-19 Test Could Show a False Result

4 Reasons Your Rapid COVID-19 Test Could Show a False Result

4 Reasons Your Rapid COVID-19 Test Could Show a False Result

gloved person inserting rapid test swab into binax now card

A COVID-19 rapid test swab is being processed.Brittany Murray/MediaNews Group/Long Beach Press-Telegram via Getty Images

  • Rapid tests are a quick and convenient way to find out your COVID-19 status.

  • Weather, temperature, and even what you eat before the test could affect your results.

  • Recent studies suggest that rapid tests detect Omicron, but only if you are using the home test correctly.

Rapid tests have become a popular tool in the coronavirus pandemic, especially during Omicron’s initial wave in 2021.

In hotspots like New York City, where infections surged, many pharmacies reported selling take-home kits containing rapid antigen tests when Omicron was at its peak. Lines were long at both test centers and sidewalk tents.

Now rapid tests are widely available. But the results you get from these tests aren’t always perfect barometers of COVID-19 infections.

Rapid tests have always been trumped by the polymerase chain reaction, or PCR, when it comes to precision. While antigen tests provide results in about 15 minutes, before the Omicron variant emerged, they were only 58% accurate for people without symptoms, or 72% accurate for people who did. based on a Cochrane review of more than 24,000 test samples. .

By comparison, a properly performed PCR test can return lab-approved results with 98% accuracy, according to the same study based on pre-Omicron data. It just takes longer to get a response, and you’re supposed to isolate yourself while you wait.

If you’re going for quick results over the waiting game, here are some things to keep in mind that could affect your test.

Home test kits have expiration dates.

At-home COVID-19 test kits are one of the most convenient inventions to come out of the pandemic. Several companies offer rapid antigen tests without a prescription, and take-home kits typically cost about $20 for a two-test pack.

While it can be tempting to stock up on home COVID-19 tests, keep in mind that kits expire in several months to a year.

Over-the-counter test kits usually have a label on the box indicating the expiration date and the date of manufacture. The later date indicates the test’s end of life, which could be sooner than expected: A BinaxNow test kit I bought at Walgreens in September 2021 expired before the end of January 2022.

Abbott, the maker of the BinaxNow kits, extended their shelf life from six months to a year in May of last year, following a review by the Food and Drug Administration. Other companies have issued similar announcements, and we may see expiration dates pushed further as the FDA continues to review stability studies.

In the meantime, home test kit users should always assume that an expired test result is incorrect.

Hot or cold temperatures can interfere with test components

The temperature at which you store your home 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.

“Don’t use rapid tests when it’s very cold. That may decrease their benefit or effectiveness,” Michael Mina, eMed’s chief scientific officer, said on a call with reporters. “You want to do it at room temperature for the most part.”

Recommended temperatures for storage and preparation can vary between tests, so be sure to check the packaging first.

The BinaxNow kit, for example, can be stored between 35.6 and 86 degrees Fahrenheit, but a fine-print warning says to make sure all test components are at room temperature before using.

What you ate for lunch could affect a throat swab

If your COVID-19 test requires a throat swab instead of a nasal swab, what you eat before getting tested could 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 Coke could cause false positives if you use an oral swab.

“You’re going to wipe your mouth after you’ve finished drinking your coffee, you’re going to get a positive result, potentially,” he said.

Anything acidic, like coffee, soda, or fruit juices, could “mess up the chemistry” of a fast flow or lateral flow test. Butler-Wu clarified that this risk is quite theoretical. One study found that false positives occurred when unexpected substances were applied directly to test kits.

But still, test sites and kits that involve oral swabs will warn you to avoid eating, drinking, and smoking for at least 30 minutes before the test. This advice may be familiar to people in the UK, where rapid tests commonly 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 lead to a false negative.

Home tests detect the Omicron variant well

It was first thought that rapid tests might not be very good at detecting Omicron, a coronavirus variant that, along with its many ramifications, has shown the ability to evade some of our immune defenses.

But, that is no longer the case.

According to a March study, rapid home tests “are not inferior among people infected with the Omicron variant of SARS-CoV-2 compared to the Delta variant.”

That is if you use the rapid test correctly and wait at least three to five days from a COVID-19 exposure to take a sample.

Last December, it was confirmed that the Abbott BinaxNow and Quidel QuickVue antigen tests appeared to detect Omicron as accurately as other variants, according to laboratory studies and an FDA review.

The same review found that diagnostic tests from Applied DNA Sciences, Meridian Bioscience, and Tide Laboratories were more likely to give false negatives due to ineffective detection of the Omicron variant.

Read the original article on Business Insider

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