Health.com: Why Even a Faint Line on Your Rapid Test Still Means You’re COVID- Positive

Health.com recently interviewed Eric Vail, MD, director of Molecular Pathology, about the at-home antigen test for the virus that causes COVID-19 and how it determines whether the virus is inside the body and, if so, how much virus is there.

At-home antigen tests work by detecting whether the virus is found in testers’ nasal secretions, Vail told Health.com. If the window on the testing stick shows two lines, the tester is positive for COVID-19.

The opaqueness of the lines also can indicate more, Vail said.

If the line is fainter, the patient is likely to be less sick, less infectious, or might be nearing the end of infection, Vail said. A faint line also can mean the tester didn’t swab well enough to provide a good test sample. A brighter line indicates the patient has more virus in their body and is likely to be sicker and more infectious.

Still, whether the line or lines are bright or faint, two lines still mean positive, one line still means negative, and the safety precautions remain the same: "Five days of [isolation] and then five days of masking if you have no symptoms,” before going back to your normal routine, Vail said.  

After following those guidelines from the U.S. Centers for Disease Control and Prevention (CDC), there’s still the possibility that someone could test positive. On day six, about 50 percent will still test positive.

“Does that mean they're still infectious? We don't know," Vail told Health.com. That uncertainty is why  the CDC recommends five more days of isolation. 

The chance of getting a false positive is low with at-home tests, so following the antigen test directions and CDC guidelines to the letter prevents the possibility of spreading the virus to others.

Click here to read the complete article from Health.