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

person wearing glove puts quick test swab into binax card now

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

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

  • Time, temperature, and even what you eat before the test can affect your results.

  • Recent research suggests that rapid tests detect Omicron, but only if you use the test correctly at home.

Rapid tests have become a popular tool during the coronavirus pandemic, especially during the first wave of Omicron in 2021.

In hot spots like New York, where infections have skyrocketed, many pharmacies reported selling out take-home kits containing rapid antigen tests as Omicron hit its peak. Queues were long both at the test centers and in tents on the sidewalks.

Now rapid tests are widely available. But the results obtained from these tests are not always perfect barometers of COVID-19 infection.

Rapid tests have always been inferior to polymerase chain reaction or PCR tests when it comes to accuracy. While antigen tests provide results in about 15 minutes before the Omicron variant came along, they were only 58% accurate for people who didn’t have symptoms and 72% for those who did, according to a Cochrane review of over 24,000 test samples .

In comparison, a properly performed PCR test can yield lab-validated results with 98% accuracy, according to the same study based on pre-Omicron data. The answer just takes longer – and you should isolate yourself while you wait.

If you decide to go for quick results instead of waiting, here are some things to keep in mind that may affect your test.

Home test kits have expiration dates

Home tests for COVID-19 are one of the more convenient inventions that can come out of the pandemic. Many companies offer over-the-counter antigen rapid tests, and take-home kits often cost around $20 for a two-test package.

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

Over-the-counter test kits usually have a sticker on the box indicating the expiration date and the date of manufacture. The later date indicates the end of the test’s shelf life, which may be sooner than expected – the BinaxNow test kit I purchased from 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 last May, following a review by the Food and Drug Administration. Other companies have made similar announcements, and it’s possible the expiration dates will be pushed back as the FDA continues to review stability studies.

In the meantime, users of home test kits should always assume that an expired test result is invalid.

High or low temperatures can damage test components

The temperature at which you store your home test kit matters.

The small vials of liquid to be mixed with the sample are not designed to withstand extreme temperatures or humidity.

“Don’t use rapid tests when it’s really cold. This may reduce their benefits or effectiveness,” said Michael Mina, eMed’s chief scientific officer, in a telephone conversation with reporters. “Mostly, you want to do it at room temperature.”

Recommended storage and preparation temperatures may vary from test to test, so check the packaging first.

For example, the BinaxNow kit can be stored between 35.6 and 86 degrees Fahrenheit, but a warning in the fine print says to make sure all test items are at room temperature before use.

What you ate for lunch can affect your throat swab

If your COVID-19 test requires a throat swab instead of a nasal swab, what you eat before taking the test can also affect the quick results.

Susan Butler-Wu, who directs infectious disease clinical research at the University of Southern California, told Insider that coffee and coca-cola can cause false positives if you use a mouth swab.

“You’re going to take a mouth swab after drinking coffee, you’ll potentially test positive,” she said.

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

Still, test sites and mouth swab kits 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 usually require a throat swab in addition to a nasal swab.

You should also avoid brushing your teeth or using a mouthwash before taking a throat swab, as good oral hygiene can temporarily remove the virus from your mouth and lead to a false negative result.

Home tests detect the Omicron variant well

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

But that’s not the case anymore.

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

This is if you use the rapid test correctly and wait at least three to five days after exposure to COVID-19 to take a swab yourself.

Last December, it was confirmed that Abbott’s BinaxNow and Quidel QuickVue antigen tests appear to detect Omicron as accurately as other variants, according to laboratory testing and an FDA review.

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

Read the original article in Business Insider

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