Is a faint line on the COVID-19 test really positive? Here’s how to interpret the results

Is a faint line on the COVID-19 test really positive?  Here’s how to interpret the results

This summer, after more than two years of avoiding COVID-19, I tested positive at a home rapid test. The line was barely there, it was so faint it didn’t even show up in the photos. Was I kidding myself? Unfortunately not. I had another test the next day, which came back with a much darker line and confirmed that I had COVID-19.

The whole experience got me thinking about how confusing it can be to run a rapid test, especially if your results seem ambiguous like mine. I also began to wonder what the tests actually measure, what that line really means, and whether a darker or lighter positive line on a COVID-19 test can tell you something about your individual infection.

With so many people using rapid tests at home, it’s crucial to learn more about how the tests work and what to do if you get questionable results. For example, testing at the right time and isolating when you test positive can help stop the spread of the virus as we adjust to this. new phase of the pandemic. Furthermore, with the recent return to school in person, emerging variants on the horizon and a potential “tripledemia” coming fastwe are likely to get more and more tests for COVID-19.

Rapid tests can even be helpful before you get your updated COVID-19 booster vaccine, experts told TODAY. If you develop symptoms that could be due to the coronavirus, for example, it’s worth consulting with an at-home test before going to your vaccination appointment. In that case, if your results are positive, you should wait to get your booster until your isolation period is over and you are no longer sick, the Centers for Disease Control and Prevention tell.

and if you have side effects after your vaccine – such as fever or muscle aches – that do not go away in a day or two, you can have a rapid test to see if you really may have a COVID-19 infection.

Here’s what you need to know to accurately interpret those results, even if they’re a bit tricky to parse.

What does the line actually measure on a COVID-19 test?

At its most basic level, the positive line on a home rapid test “it shows the presence of specific viral proteins,” Omai Garner, Ph.D., clinical associate professor and director of clinical microbiology at UCLA Health, told TODAY.

“You’re looking for a particular part of the virus that sticks to test components that bind to a color,” Dr. Emily Volk, president of the College of American Pathologists, told TODAY.

From there, the proteins “get caught on that line and show a band of color,” Dr. Amy Mathers, associate professor of medicine and pathology and associate director of clinical microbiology at the University School of Medicine, told TODAY. of Virginia.

If that positive line appears, it is very likely that you have coronavirus proteins in your nose, and that you have covid-19.

Does a faint line count as a positive result?

Yes, the experts said.

“It’s not a super sensitive test, which means you have to have a fair amount of virus in there just for the home antigen test to work,” Garner said. He notes that “any line early in the infectious process implies that someone is highly contagious.”

But that doesn’t mean it’s always easy to read. “Sometimes it’s not exactly a line; it can be like fluff,” Mathers said. “But if you see a line there, it’s there.”

It can also be helpful to take into account the context of what is happening around you. If COVID-19 transmission levels are high in your area, if you know you were exposed to someone with the infection or if you have noticeable symptoms, all of these are good reasons to interpret a maybe positive as definitely positive.

To confirm the result, the Food and Drug Administration recommends performing another rapid test 48 hours later. If you have symptoms that could be COVID-19 or know you were recently exposed to COVID-19, the FDA recommends getting another test 48 hours later.

If there’s any confusion during the process, you can also skip the rapid repeat tests and go straight to your doctor or get a PCR test, the FDA says. However the CDC notes that people who have had COVID-19 can continue to test positive on PCR tests for up to 90 days, so it can be difficult to use a PCR test to diagnose a new coronavirus infection.

If you took antiviral medications, such as Paxlovid, you may test positive just a few days after getting a negative result. This is a phenomenon called Paxlovid rebound or rebound of COVID-19. Sometimes people’s symptoms return along with the positive rebound test, but not always.

The only situation in which you wouldn’t assume a faint line on a rapid test is positive is if it turns positive after the allotted testing period, Garner said. “If you left the test for two hours, you can have a false-positive junction,” she explained. “But if the test is done correctly, any line, no matter how faint, is a true positive.”

Also, keep an eye on the expiration date of the rapid tests you are using. If you use a home test after its expiration date, you may not get accurate results. the FDA has information about shelf life and expiration dates, including some that have been extended for several months, for all the home tests you have authorized.

Does it matter if the line on your COVID-19 test is very dark?

In theory, “the more viral proteins there are, the darker the line will be,” Garner said. And from there, you might conclude that you are more or less contagious or that you might have a milder or more severe infection depending on how dark or faint your line is.

But these tests weren’t actually designed to measure any of that, experts said. “These antigen tests … are not designed to give an estimate of ‘Is there a lot of virus or is there a little virus?'” Volk explained.

They are really meant to be read as a binary: positive or negative.

“We have some of these tests in our lab that we run as medical tests, and we don’t interpret the strength of the (line) at all,” Mathers added. In addition, there are many other reasons a test line might be darker or lighter that have nothing to do with the actual amount of viral particles in your body, he said.

For example, the consistency of the mucus in the nose can affect how much of those viral proteins accumulate. “So you may have a viral antigen load in your nose,” but that may not be an accurate reflection of how much virus is actually circulating in your system because your mucus is so thick, Mathers explained. (Mucus, like saliva, can be thicker or thinner depending on how hydrated you areshe said.)

Also, the pH of your nasal ecosystem “could change how well the virus binds,” he said. “All of those variables in human specimens can alter how the test reads.”

The ambient temperature when you test, as well as how the tests are stored, can also affect the results, as TODAY explained above.

We know that early in infection, people can be very contagious and have a lighter line on their rapid antigen test, or not be positive at all. they can even have symptoms for a few days before testing positive. “People can have severe COVID infections and a weak line, and people can have mild COVID infections and a very deep red line,” Volk said.

With the convenience and availability of rapid tests, it’s understandable that people want to use them in ways that aren’t necessarily intended, Garner said. “People are trying to use antigen tests not only to help diagnose the disease, but also to help their behavior after they’ve been infected.” That is especially true in those difficult situations where people may be pressured to return to work. or have to make difficult decisions about participating in other activities, even if they are still testing positivehe said.

But you shouldn’t use the lightness or darkness of the line in your test to direct its behavior because the tests simply aren’t designed or FDA-cleared for that, Volk and Mathers agreed.

If your line is lighter, for example, that doesn’t mean you can ignore other precautions, like masking. “You can’t really get actionable information (by looking at whether your line is lighter or darker),” Volk explained.

If it’s positive, it’s positive, and you can probably leave it at that.

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