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Why you may not want to trust your negative at-home COVID-19 test

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Youngstown City Health Department worker Faith Terreri grabs two at-home COVID-19 test kits to be handed in Youngstown, Ohio.

Youngstown City Health Department worker Faith Terreri grabs two at-home COVID-19 test kits to be handed out during a distribution event, Dec. 30, 2021, in Youngstown, Ohio. So you’ve taken a home test for COVID-19 and it’s negative. That means you’re virus-free, right? Maybe. Maybe not.

David Dermer, Associated Press

So you’ve taken a home test for COVID-19 and it’s negative. That means you’re virus-free, right?

Maybe. Maybe not.

You may still be sick and able to spread the disease that continues to cause rising case counts, hospitalizations and deaths in Utah, including the loss of 19 lives to COVID-19 in the state during the final week of June, according to the Utah Department of Health and Human Services.

Swabbing to see if symptoms like the sniffles or a fever are COVID-19 rather than allergies, a cold or the flu has become routine for many Utahns, even if they’re fully vaccinated and boosted, but the rapid antigen tests available for home use need to be used properly to get the most accurate results, experts say.

For starters, there’s a reason the tests are packaged two to a box. You’re supposed to double-check the initial result with a follow-up test within a day or two, said Han Kim, a professor of public health at Westminster College in Salt Lake City.

“They recommend doing it twice,” he said, even though studies suggest most people only take one of the two tests in the home kit. “That’s why these tests come in two. That’s not to test two times in the next month. It is really for a single test.”

The reason for swabbing a second time is that even if you are starting to feel sick or have just been exposed to someone with COVID-19, you may not yet have enough of a viral load for there to be a detectable amount of antigens, the proteins resulting from the infection, Kim said.

So if you take the test too soon, there’s the risk of getting a false negative result.

But the omicron variant, which fueled last winter’s record-breaking surge in cases in Utah and the rest of the country and has since mutated into new subvariants that continue to spread, does have a quick incubation period of only two to four days, so waiting too long to test isn’t a good idea, either.

“That’s the trick,” Kim said, of timing a home test just right, and why another test is necessary.

Other issues with rapid antigen tests done at home include user error. The swabs must be inserted far enough in the nasal cavity to collect enough antigens. The sample must be stirred enough in the provided solution, dropped in the right place on the test strip and the results read correctly.

There’s always the possibility of getting a faulty test kit, too.

The other option for testing for COVID-19 is a PCR, or polymerase chain reaction, a more accurate test that can identify an infection sooner since it looks for the virus itself. But a PCR test must be done through a health care provider and sent to a lab for processing, so it can take a day or more to get results.

Kim said anyone whose first at-home test is positive should assume they have COVID-19 and take precautions, like wearing a mask and avoiding others for at least five days. Even those who initially test negative might want to do the same until they’re cleared by a second negative test, he said.

And ideally, any positive at-home test should be followed up by a PCR test, Kim said, because while rare, false positives are possible. Plus, the results of at-home tests are not reported to authorities and may not be accepted when required for travel or other purposes.

Dr. Emily Spivak, an infectious diseases physician with University of Utah Health, experienced firsthand the issues with home tests when she had COVID-19 in mid-May.

“I had two or three days of pretty significant symptoms with a rapid (test) that was negative. I think on that second or third day, I said to my husband, ‘I need to do a PCR because this doesn’t make sense,’” Spivak said. Sure enough, her PCR test was positive.

“I continued to do a rapid because I was curious what was going to happen. And my rapid the very next day turned positive. Like very positive, very quickly,” she said, adding that’s not going to be true for everyone. One of her daughters tested positive using a home test kit within 12 hours of showing symptoms.

“It is definitely possible to be symptomatic with COVID and your rapid test is initially negative,” Spivak said, recommending that people with symptoms get a definitive answer from a PCR test or plan on doing daily rapid tests while their symptoms persist to see if they eventually test positive.

Rapid tests are more effective in people with symptoms, she said, but may still yield a false negative result within the first 72 hours or so of signs of the virus showing up. Try again in a day or two, Spivak said, urging everyone to read the directions that come with the home kit, and watch for faulty tests.

“I had one that was faulty. I’m not sure if I did something wrong, but it never started to flow up. I don’t know if I didn’t drop enough drops, or messed them up in the wells, but it’s like the wetness, the moisture, never went up,” the doctor said, adding she knows of others who’ve had similar trouble with the kits.

“It’s not common, but it definitely can happen,” Spivak said.

Home test kits can be pricey to purchase, costing 20 times the $1.25 that Kim regularly saw them available for during a recent trip to Asia. The U.S. government is offering a third round of free at-home COVID-19 tests through the mail, but future funding for the administration’s virus response remains hung up in Congress.

Utahns were encouraged to stay away from overwhelmed free mass testing sites during the height of the omicron surge and the state later shifted most testing for the virus to private providers under the “steady state” approach taken by Gov. Spencer Cox that treats COVID-19 more like the flu or other endemic diseases.