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Which COVID test is more accurate? It depends on what you're testing for

The rapid test gives you a negative. The PCR gives you a positive. They can both be right. Here's why...

GREENSBORO, N.C. — You took two COVID tests: One is a rapid at-home test, and it's negative. One is a PCR test, done through a clinic and a lab, and it's positive. Is one of the tests wrong? The Chief Science Officer for a Biotech software company says..."No."

“It looks like the rapid test is failing, but it is actually more accurate in telling us what we want to know and are interested in, which is, am I at risk to my neighbors, do I need to isolate,” said Dr. Michael Mina, Chief Science Officer, eMed and an Epidemiologist.

Let's explain.

The PCR test can detect the virus in your body for weeks. It's that sensitive. This calendar example shows a positive result for 16 days.

Credit: WFMY

The rapid test will only give you a positive when you are infectious. So, in this example, the same person could test negative in five days versus 16. This means they are only infectious and need to isolate for those first five days.

“We should really start leaving the PCR test to what it's best for - medical, clinical diagnosis by a doctor, and allow the rapid tests to be for public health - do I need to isolate and take action,” said Min, who talked to CBS This Morning. 

When it comes to the at-home test kits, you need to follow the instructions carefully. It can be easy to mess up, but reading the line for positive or negative should be easy.

“If the line is very, very dark, you know you have a lot of replicating virus in you, you're likely very infectious. If the line becomes very faint, you could be at the beginning of the end of your infection, so that is when it becomes important to have a second test that you can repeat, say 24-48 hours later,” said Mina.