2022-03-23 09:06:35

What does a faint line on your COVID antigen test mean?

Copyright & credited by SFGATE
https://www.sfgate.com/news/article/faint-line-on-COVID-antigen-test-17001818.php

It's a common scenario for anyone who has tested positive for COVID-19 and spent several days in isolation.
 
You’ve tested positive for COVID, done the responsible thing and isolated. Now it’s day 5, and you excitedly stick a rapid test swab up your nose and swirl it around. Then you wait around for 10 or 15 minutes (depending on the test directions), eagerly checking on your get out of jail card. But when your phone timer goes off, you check it and see two lines, and the positive line is very faint — much less visible than when you first tested. Then you test again the next day, and that positive line seems to be even more faint than it was on day 5. You have to put on your reading glasses to see it.
 
You may want to believe the faint line indicates that your body is shedding less virus particles out into the universe (and maybe it’s OK to go to that party after all?).
 
Sorry to be a party pooper, but according to experts, you should still assume you're positive and continue to isolate yourself. The California Department of Public Health requires that if you test positive, you isolate at least 5 days. If you test negative on day 5 or any day after, you can end isolation. On day 11, isolation ends, even if you're still positive.
 
Rapid antigen tests use the well-established lateral flow technology (think home pregnancy tests) to detect viral proteins, or antigens, in your snot. They’re a great technology for public health because they provide fast results and can give you results at home. They’re also offered at some testing sites, especially ones that test a lot of people. (You can order free tests through the government at COVIDtests.gov, or find them at pharmacies and online retailers. If you’re insured, you’re probably eligible for reimbursement.)
 
Dr. Stephen Miller, the director of UCSF's clinical microbiology laboratory, said the antigen tests weren't designed to be "quantitative" — as in, to detect the quantity of virus in your system — but “qualitative.” That means they really only give yes or no answers, according to Miller, who knows firsthand that there are several factors that go into performing these tests correctly, and that following the instructions is important for reliable results.
 
It’s hard to know what causes a faint line. One possibility is that you do, in fact, have a smaller volume of virus particles in your snot, said UCSF infectious diseases expert Dr. Peter Chin-Hong. But that doesn’t necessarily mean you’re less infectious. The tests, after all, weren’t designed to tell you anything beyond whether you’ve got a detectable viral load.
 
Either way, if you have enough particles in your nose to get any kind of line — faint or not — there’s a decent chance you’re still shedding enough live virus to give somebody else COVID-19, especially if you’re still feeling sick. "The level of virus needed to cause a positive antigen test, at least for patients who are acutely symptomatic, appears to have some reasonable correlation with infectiousness," Miller said.
 
Unfortunately, plenty of people who get a negative rapid test will go on to infect other people. That’s especially true if you don’t have any symptoms. So if it’s really, really important that you don’t have COVID — like if you want to have dinner inside with your elderly grandmother or a severely immunocompromised friend — it’s better to be safe than sorry and wait until you get a negative result on a more sensitive test, meaning a PCR or molecular diagnostic assay.
 
These tests are more accurate, but they take longer and cost more. They’re also much more likely to give you a positive result after you're no longer infectious. "The antigen test gives us a better idea about transmissibility," Chin-Hong told SFGATE for a previous story.
 
The good news is, even if you get a positive rapid test result on day 11, you can still end your isolation, according to the California Department of Public Health.
 
"The research shows that by day 11, it's pretty certain that you're no longer infectious, regardless of what the test shows," Miller said. "Your likelihood of being infectious, it's not necessarily going to be zero, but it's going to be quite low. So the benefit of people being able to leave isolation, go back to work and go back to school, outweighs low infectiousness."

 

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