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Your COVID-19 antigen test result shows a faint line. Here's what it could mean

Many COVID-19 rapid antigen tests come back with a faint positive line. Does that mean anything?

WASHINGTON — One of the quickest ways to know if you have COVID is the rapid tests. If you are positive, a line appears on the test kit.

However, you may have noticed that line can be bold or faint. Does that mean anything? We went to the experts to Verify.

QUESTION:

Does the faintness of a line on an antigen test tell you anything about how contagious you are, or if the virus is on its way out?

OUR SOURCES:

  • Dr. Amesh Adalja, Senior Scholar at Johns Hopkins University
  • Dr. Gigi Gronvall, Senior Scholar and Associate Professor at Johns Hopkins University
  • Dr. William Morice, Chair of Mayo Clinic’s Department of Laboratory Medicine and Pathology and President of Mayo Clinic Laboratories

ANSWER: 

This is false.

No, our experts say the faintness of the line doesn’t tell you much.

WHAT WE FOUND:

Our experts all agreed:

“If your test is positive, irrespective of the faintness on an antigen line, you should consider yourself contagious and infected,” Dr. Adalja said.

So, what does the faintness of the positive line mean?

“There's a lot of reasons why that line could be faint,” Dr. Morice. “One could be you don't have much virus in there, another could be poor reactivity, another could be [a] poor specimen.”

“You're positive, you're still producing virus,” Gronvall said.  “It's interesting, but does it make a difference? We don't know exactly how much virus you need to transmit to somebody else.”

So basically, all the experts agreed the faint line "could" mean you have less of the virus in your system. But we don’t know. The tests aren’t designed to measure viral loads. They also could be faint because of a problem with the test either from a bad test or user error.

“If you're positive, treat it as a positive, irrespective of how bright or faint it is,” Dr. Adalja said. Think of it as positive until it is unequivocally negative.”

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