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False positives? Here's what's causing accuracy issues with some coronavirus tests

So if your nasal swab was tested by Becton, Dickinson and Company, that same sample might need to be rerun in the lab.

NEW ORLEANS — You may be hearing from your doctor that the coronavirus test you got is a false positive. That means you were told you are infected, but you really are not. So why is this happening and what should you do about it?   And what is causing a false negative?

You've waited in line for hours to get that uncomfortable nasal swab to see if you are infected with the SARS-2 coronavirus. Then it comes back positive, but you feel completely fine. Tulane's Dr. Robert Garry, who's worked on the Ebola virus and the original SARS virus, says there could be a few explanations. First, let's say you truly are infected. 

"Usually if they do have it, they're going to be OK," said Dr. Robert Garry, a Professor of Microbiology and Immunology at Tulane Medical School. 

That's because many people don't get symptoms, but you will need to stay away from others for at least two weeks to stop the spread.

Next, you could be one of the people who was not infected and the test gave you a false positive.

"The FDA is trying to tell us that this SARS-CoV-2 test by BD
gives some false positives. Now, it's a fairly low rate. It's only three percent." he explained.

So if your nasal swab was tested by Becton, Dickinson and Company, that same sample might need to be rerun in the lab.

"If they were using this particular test, then they'll go and they'll say, 'Hmmm, we probably need to rerun that on another assay from another manufacturer just to make sure.'"

There's nothing you can do, but the company should rerun it to confirm.

 But now the third part is important. Let's say you go to a gathering and know you were exposed to someone who tests positive shortly afterward. Dr. Garry says you should not run out and get tested the next day or two or even three. That may give you a false negative. Why? Because it takes five to eight days for the virus to multiply to a certain level.

You're going to have enough virus in your system coming out your nose to be able to be detected by the test," Dr. Garry said about waiting several days to get the test. "Too soon, the test may not pick it up."

And Dr. Garry says if you are showing signs of being sick, let your doctor, not the test, determine if you need to be admitted to the hospital.

The FDA is now working with the company to fix the problem. Any false positive tests should be reported to that agency.

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