Why Do People Get So Many False Negatives Using At-Home COVID-19 Tests?

Jackie Kramer thought she had COVID-19 late last month.

Everyone in her family tested positive. And she had symptoms: congestion, a headache and fatigue.

Yet the Andersonville woman kept testing negative, over and over again. She took several PCR tests and rapid, at-home COVID-19 tests every day for a week.

“I don’t understand why I tested negative for a week when I had all the symptoms,” said Kramer, 56. “I’d stare at it, like, how can this be?” She spent the week isolating from her husband, 21-year-old daughter and 18-year-old son, to avoid catching COVID-19, just in case the tests were right.

Finally, after a week of testing negative, an at-home test came back positive, confirming what she had suspected — but wasn’t 100% sure of — all along. She called the experience “extremely frustrating.”

Like Kramer, many people during this surge have gotten negative results on at-home tests only to later learn that they actually had COVID-19 — a fact that comes as the federal government pushes to get more free at-home tests into people’s hands. Experts, however, say the at-home tests remain as accurate as they’ve ever been, even with the omicron variant. Rather, experts attribute the false negatives to other possible factors: no test is 100% accurate, people may not be administering them correctly, or people are testing too early to detect their COVID-19 infections.

“You should never do just one test,” said Dr. Emily Landon, hospital epidemiologist at the University of Chicago Medical Center. “There’s a reason there’s two tests in the box.”

It can take time for the amount of the virus in a person’s body to reach a high enough level that an at-home test would detect it, she said. A vaccinated person might get symptoms of COVID-19 before an at-home test would turn out a positive result, because the person’s body has already been primed to fight the infection and starts doing so with only a small amount of the virus in the body, Landon said.

Like Kramer, people who feel ill and get a negative result on an at-home test should take the tests repeatedly, as often as daily, depending on the specific test’s instructions and if they have enough tests on-hand, Landon said. If there is only one at-home test available, wait until the second or third day of symptoms to test, and if the test is negative, get a PCR test, she said.

PCR tests can detect COVID-19 for a longer window of time than at-home tests.

In recent weeks, it wasn’t always possible for people who felt ill to use at-home tests every day, given that they were tough to find on store shelves and could cost $20 to $30 a package. The federal government is now sending four free tests to each household, and health insurance companies are now covering up to eight tests per month per person, though that doesn’t apply to people on Medicare.

People should take advantage of those programs, and get plenty of tests, Landon said. If people are treating at-home tests like precious resources, they’re not using them correctly, she said.

“They’re best used regularly and in an ongoing way as we battle the pandemic,” Landon said. “If you have them on-hand like toilet paper … and stockpile them, you’re going to have enough.”

Lisa Guo knows she was fortunate to have several COVID-19 tests on-hand last month, after she was exposed to a co-worker with COVID-19.

Guo took an at-home test about two days after the exposure, and that test came back negative. The next morning Guo, 33, of Lakeview, woke with a headache, dry cough and low fever. She took another at-home test that, again, came back negative.

She began to feel frustrated, not knowing exactly what she had or how long she’d have to stay home from work.

Still feeling sick the next day, she again swabbed her nose at home. Finally, the test was positive — and she felt relieved to finally know what she had and how to proceed.

“I knew I had something and I was pretty sure it was COVID, and that’s why I kept testing,” said Guo, who was sick for about two weeks but has since recovered. She also tested repeatedly because of guidance from her father, who is an emergency room doctor, she said.

It’s possible, experts say, that not everyone understands they’re supposed to take multiple at-home tests if they feel sick and get negative results. The instructions that come with at-home tests tell people to take a second test, and explain that more frequent testing may help detect COVID-19 more quickly, but not everyone may read through all the instructions.

For Abbott Laboratory’s popular BinaxNOW test, for example, some of those directions and warnings are spelled out over four pages of fine print on the back of the instructions for administering the test.

The tests could also be producing some false positives because that’s the nature of tests, experts say. No test is perfect. COVID-19 at-home tests generally have 70% to 90% accuracy, depending on the brand, in detecting COVID-19 compared with PCR tests, which take longer to return results.

At-home tests also, generally, aren’t as effective when used by asymptomatic people, such as after an exposure, Landon said. Those people should likely get PCR tests instead, or, if they’re going to use at-home tests, take them every other day starting three days after the exposure until nine days after.

“There’s a reason we don’t routinely have medical tests available at the pharmacy — because they’re really hard to interpret,” Landon said. “You have to understand the benefits and risks of the tests, follow complex instructions and understand what to do for follow-up based on results of the test.”

Still, despite the limitations of at-home COVID-19 tests — and negative test results in people who actually have COVID-19 — experts say they’re still valuable.

“What these tests are good for is picking up the highly contagious people,” said Dr. Robert Murphy, executive director of the Havey Institute for Global Health at Northwestern University Feinberg School of Medicine.

People who test positive on at-home tests likely have so much virus in their bodies that they’re more likely to be contagious than those who test negative, even if they have COVID-19, he said.

Murphy still recommends people use at-home tests before gatherings with people outside their households.

“I test everybody, knowing it’s not such a sensitive test, but it gives me some extra reassurance that you’re going to pick out the superspreaders, the people who are highly contagious,” he said.

It can also be a good type of test for people who feel ill, if they take it repeatedly, he said. And at-home tests are preferable to sending everyone who starts coughing to get a PCR test, given that PCR tests often require appointments and can take days to get results.

At-home tests aren’t a perfect test, but they’re the best option out there at the moment for testing large numbers of people frequently, in hopes of limiting the spread of COVID-19, experts said.

“They are useful, but everything has its limitations, and this is just one tool we have,” Murphy said.