Can you rely on COVID-19 at-home tests? Here’s what you should know

More and more of us rely on self-testing to determine whether we have COVID or another respiratory illness. How reliable are these tests? When is the best time to test yourself? And what if your test kits have expired? Here's a look at what you should know about coronavirus at-home tests.

When it comes to determining whether sniffles or a cough are COVID, people now rely more heavily on at-home tests to learn whether they have the virus.  But can they trust that a self-test is providing an accurate result?

Experts say at-home rapid tests will pick up coronavirus even as new strains emerge — but a negative result doesn’t mean you don’t have COVID.

As you stick the swab up your nose, you will want to consider what the Centers for Disease Control & Prevention says about COVID testing in 2023: Positive at-home test results are accurate and reliable. A single negative antigen test cannot rule out infection.

Tests aren’t specific to variants

For now, the COVID variant has little bearing on whether rapid tests picks up the virus because they target the nucleocapsid proteins of the coronavirus, which don’t change as much as spike proteins targeted by vaccines.

“These at-home tests are designed to detect the part of the virus not affected by genetic changes that produce a new variant,” explained Dr. Nicole Iovine, chief hospital epidemiologist at UF Health Gainesville  “These are still good tests and will detect the virus even as it keeps mutating itself.”

Iovine compares the COVID rapid test to the one for influenza. “Every year, different strains circulate but tests are still able to pick it up,” she said.

Timing is key

Three years into the pandemic, some people no longer want to know if they have COVID, brushing mild symptoms off as a cold or allergies. But you never know when you come in contact with high-risk people such as senior family members or co-workers who are immunocompromised, and testing can help guide your behavior. And if you are sick enough, you may want to get an antiviral like Paxlovid.

When you test yourself at home, testing too soon can affect the result.

If you have symptoms and your at-home test comes back negative, that doesn’t mean you don’t have COVID.  You might have tested before virus levels were high enough to be detectable. If you are feeling congested, achy, or have a sore or scratchy throat, and your test is negative, you should take a second test 48 hours later, according to FDA recommendations.

Now that our immune systems recognize the virus, people get symptoms sooner than they used to and might test themselves before the virus has a chance to build up enough copies to show a positive result, immunologist Michael Mina, chief science officer at the telehealth company eMed, told CNN.

“So people are now starting to test really fast, like day one, day two post-exposure, when we know that the average person won’t get a viral load that’s high enough to be detectable on PCR or antigen tests until day 3, 4, 5 or 6,” Mina told CNN.

What to do if you have been exposed

“Testing should be based on symptoms and risk,” said Dr. Dushyantha Jayaweera, an infectious disease expert with UMiami Miller School of Medicine. “If you have symptoms suggestive of COVID, you should test yourself. It should not be based on when you were vaccinated or last infected, but rather on how you feel right now.”

If you were exposed to COVID but don’t have symptoms, the U.S. Food and Drug Adminitration advises to wait at least five days before testing, because swabbing too early can give you a false negative.

Jayaweera says to consider the type of of exposure: If you had prolonged exposure to someone who has COVID but don’t have symptoms, wait a few days and test.

Roughly 30% of people test positive within three days after an exposure, another 30% to 50% within five days after, and about 20% test positive around day six or seven, according to Mina.

If you have been exposed and test negative, the FDA recommends you repeat the test two more times, 48 hours apart. You want will to take precautions around anyone who is immune-compromised until after your third negative test result.

PCR tests remain the most accurate for confirming you have the virus. You can still get them done by health providers and processed in a lab. Results can take up to 24 hours.

Where can I get an at-home test?

Four free at-home COVID-19 tests are available by mail through the federal government at COVID.gov/tests.

However, if you have symptoms or were exposed and want to self-test right away, check your local pharmacy. Some private health insurance may reimburse the cost of self-tests. Retailers like Publix and Walmart carry different brands of the tests and usually stock them near the pharmacy window.

Expired tests may lead to inaccurate results

If you have tests lying around your home from last year, the FDA  has a list, by name, of all the at-home tests that show whether they have expired or if their expiration date has been extended. Be sure to check the At-Home OTC COVID-19 Diagnostic Tests website.

But why take a chance? If the test has expired, you can’t always trust the result, Iovine said.

Are at-home tests less reliable  for children?

It’s possible they are less reliable.

In a study done of 426 children in Taiwan, rapid tests often read as negative when the child was positive. A PCR test was used to confirm their positive result. In this study, the negative predictive rate was accurate only 38% of the time. Researchers believe test results may have been skewed by the difficulties parents have in getting a nasal swab from a squirmy child.

When should you retest after having COVID?

If you test positive for COVID-19, CDC guidelines say you should stay home for at least five days and isolate from others in your home. You are likely most infectious during these first five days. If you still have symptoms you should come out of isolation only after you are fever-free for 24 hours (without the use of fever-reducing medication like Tylenol) and if your symptoms are improving.

Often, people want to ensure they are COVID-free by retesting, but it can take up to 10 days (or longer) to get a negative result, according to immunologists. Workplaces rarely require anymore a negative result to return to work.

“We know that a rapid test can pick up viral particles that might not be active,” Iovine said. “It’s best to go by the symptoms.”

“But if you are medically fragile or going to be more around someone who is vulnerable, rather than testing again, take additional precautions,” she said.

Sun Sentinel health reporter Cindy Goodman can be reached at cgoodman@sunsentinel.com.