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What to know about COVID-19 testing

A hand wearing a medical glove holding an illustration of the COVID-19 virus.

There are three kinds of tests for the virus that causes COVID-19—and they're used in different ways to help fight the pandemic. Here's how they work, according to the Centers for Disease Control and Prevention and the U.S. Food and Drug Administration (FDA):

Serology testing

This is a blood test that looks for signs of antibodies in your blood. Antibodies are proteins your body makes in response to infections. If you have antibodies to the coronavirus, that means that you have had the virus, even if you didn't have any symptoms.

This kind of test can help scientists estimate how many people in the U.S. have had the virus. But it's not the best test to diagnose COVID-19. That's because it can take one to three weeks for you to develop antibodies. So they might not show up on a serology test early in your illness.

So why do this kind of test at all? It can be an important guide to help researchers and policymakers understand how many people have had the virus. Or if you're experiencing long-term effects or want to donate convalescent plasma, it may help doctors confirm a past infection.

Even if you don't think you've been sick, you might be asked to take a serology test if you live in an area where a lot of people have been affected by COVID-19.

Molecular testing

Molecular tests look for genetic signs of the virus.

To do this test, your doctor swabs the inside of your nose and the upper part of your throat. It takes just a few seconds to collect a sample, which is then tested in a lab. A saliva test may also be available.

Molecular tests are highly accurate. So they're one of the most reliable ways to diagnose COVID-19. But it may take several days to get the results back from a lab. So there's another test you might receive first.

Antigen testing

Antigen tests look for fragments of proteins that are found in or on the coronavirus. 

These tests use a nasal or throat swab. And they can give results in minutes at a doctor's office, rather than having to be sent out to a lab.

This may be the first test you're given if your doctor suspects you have COVID-19. But antigen tests are not as accurate as molecular tests. They don't always detect the virus. That's why, if your antigen test is negative, doctors may want to follow up with a molecular test to be sure you don't have COVID-19.

What about at-home tests?

Test kits are available that allow you to collect your own samples at home—either by doing your own nasal swab or by collecting your saliva. Some have to be sent to a lab for molecular testing. Others are antigen tests that can give you the results at home. 

Who should get tested?

CDC recommends that anyone with symptoms of COVID-19 be tested, even if they're fully vaccinated. Others may need testing too if they've been exposed to COVID-19 or taken part in high-risk activities. Ask your doctor if it's right for you.

What is pooled testing?

To help implement more widespread testing of people without symptoms, your doctor may do something called pooled testing. That means your sample would be combined with others to be tested as a group.

If a pooled test is negative, then everyone in the group can be cleared. If a pooled test is positive, then each person in the group needs to be retested individually to find out which ones have the virus.

For more COVID-19 information, visit the Coronavirus topic center.

Reviewed 7/6/2021

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