Is a faint line on the COVID-19 test actually positive? Experts explain how to interpret results
Is a faint line on the COVID-19 test actually positive?  Experts explain how to interpret results

Is a faint line on the COVID-19 test actually positive? Experts explain how to interpret results

A few weeks ago, after more than two years of avoiding COVID-19, I tested positive on one home quick test. The line was barely there – so faint that it did not even appear in pictures. Have I cheated on myself? Unfortunately not. The much more overtly positive test I took the next day confirmed that I had COVID-19.

The whole experience also made me think about what the streak actually means and whether a darker or lighter positive streak on a COVID-19 test can tell you something about your individual infection.

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

At its most literal level, the positive line is on one quick test at home “demonstrates the presence of targeted viral proteins,” Omai Garner, Ph.D., associate clinical professor and director of clinical microbiology at UCLA Health, told TODAY.

“It looks for a specific part of the virus that binds to components in the test that are attached to a dye,” said Dr. Emily Volk, President of the College of American Pathologists, to TODAY.

From there, “the proteins are captured on that line and show a ribbon,” Dr. Amy Mathers, Associate Professor of Medicine and Pathology and Associate Director of Clinical Microbiology at the University of Virginia School of Medicine, TODAY.

If the positive line shows up, it is very likely that you have coronavirus proteins in your nose – and that you have COVID-19.

Does a weak line count as a positive result?

Yes, said the experts.

“It’s not a super-sensitive test, which means you have to have a good amount of viruses there just to make the home antigen test work at all,” Garner said. With that in mind, “anyone line early in the contagious process implies that someone is highly contagious. “

But that does not mean that it is always easy to read. “Sometimes it’s not quite a line; it can be like a fuzz,” Mathers said. “But if you see a line there, then it’s there.”

It can also help to take in context what is happening around you. If COVID-19 transmission levels are high in your area (as they are in large parts of the country right now), if you know you have been exposed to someone with the infection, or if you have noticeable symptoms, it’s all good reasons to interpret a perhaps-positive as an absolute-positive.

“Especially with the amount of COVID circulatingit should be considered positive until proven otherwise, “Mathers said.

If you want to confirm the result, you can take another quick test a day or two later. If your second test is also pretty weak, or you do not have a dash at all, this is a good time to take a PCR test to see what is really going on, Garner said. Both Volk and Mathers suggest that people who are unsure of their results skip the second quick test and go straight to their doctor or a PCR test.

The only situation where you would not assume that a faint line on a quick test is positive is if it became positive after the allotted test period, Garner said. “If you just left the test for two hours, you could have a false positive bond,” he explained. “But if the test is performed correctly, every line – no matter how weak – is a true positive.”

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

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

But these tests were not really designed to measure any of it, experts said. “These antigen tests are qualitative, so they are not designed to give you an estimate of, ‘Is there a lot of virus or is there a little virus?'” Volk explained.

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

“We have some of these tests in our lab that we run as medical tests, and we do not interpret the strength of (the line) at all,” Mathers added. Plus, there are a lot of other reasons why a test line may be darker or lighter, which has nothing to do with the actual amount of viral particles in your body, she said.

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

Additionally, the pH of your nasal ecosystem could “change how well the virus binds,” she said. “All of these variables in human samples can change the way the test can read.”

The room temperature when you run the test, as well as how well the tests are stored, can also affect the results, such as TODAY explained earlier.

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

With the convenience and availability of quick tests, it’s understandable that people will use them in ways they are not necessarily intended for, Garner said. “People try to use the antigen tests not only to help diagnose disease, but also to help with their behavior after they have been infected.” This is especially true in the difficult situations where people may be pressured to return to work ASAP or have to make difficult decisions to participate in other activities – even if they still test positivehe said.

But you should not use the lightness or darkness of the line on your test to control your behavior because the tests are simply not designed or FDA-authorized for it, Volk and Mathers agreed.

For example, if your line is lighter, it does not mean that you can ignore other precautions, such as masking. “There really is no useful information to retrieve (from looking at whether your line is lighter or darker),” Volk explained. If it’s positive, it’s positive – and you can probably not.


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