COVID-19: Viral Testing

It’s a good idea to get tested for COVID-19 when someone has symptoms of the infection or if they were around someone who is infected. Test results can reassure them that they’re probably not infected — or can tell them they need to isolate until the infection passes. Here’s a summary of the available viral tests.

What Are the Types of Viral Tests for COVID-19?

Viral tests look for pieces of the virus in a person’s nose or mouth. They can tell if the person is infected on the day of the test. This is why they’re also called “diagnostic tests."

The two main types of viral tests are:

Molecular Tests (such as PCR)

• What is tested? These tests detect the genetic material of the virus, which is called RNA.
• How is the test done? Molecular tests usually involve a swab from the nose, but may sometimes use a swab from the mouth or throat, or even saliva (spit).
• How long does it take? The sample is usually sent to a lab. Results can take 1–3 days or longer depending on how many tests the lab has to run. Some molecular tests can be ready very quickly, in 1–2 hours.
• What are the pros and cons? Molecular tests are very sensitive. This means that they can detect very small amounts of virus in someone’s nose or throat. Someone at the very beginning or very end of their illness may have only a small amount of virus, but this will still be picked up on a molecular test. This means the test can work well to detect the virus throughout the duration of the illness. But the high sensitivity can be a problem too. These tests can detect inactive pieces of the virus that stay in the nose or throat for weeks after the person is no longer contagious. A long wait for results also can be a problem if someone needs to know if they’re infected on the day of the test.

Antigen Tests

• What is tested? These tests look for proteins on the surface of the virus.
• How is the test done? Antigen tests usually use a swab from the nose or throat.
• How long does it take? The test is usually done on the spot, with results available in 15–30 minutes.
• What are the pros and cons? Antigen tests provide results very quickly, which is why they're often called “rapid” tests. This is helpful when someone is deciding if it’s safe to attend school, work, or gatherings with other people, as they can show right away if the person is infected. Antigen tests are less sensitive than molecular tests, because they need more of the virus present to detect infection. But if the question is whether a person is infected and contagious, antigen tests can work really well. People who are contagious generally have lots of virus in their nose and throat, so they don’t require a very sensitive test. If an antigen test does not pick up the virus the first time it’s done, it can help to repeat it a day or two later. If a person is infected, the antigen test will eventually detect the virus when the levels in the nose and throat increase.

Talk to your doctor to see if COVID-19 testing could be helpful for you or your family.