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COVID-19 Testing: PCR and Antigen

There are two types of tests to determine if you are positive for COVID-19 infection: PCR and antigen. Here, we clear up the confusion to help decide which test is best for you.

  • PCR tests detects viral RNA. It's usually the type of test you take at a COVID-19 testing center or at a doctor's office. This is performed by either collecting your saliva by spitting in a tube or through a nasal swab. The turnaround time usually takes about one to two days.
  • Antigen tests (rapid tests) detect proteins that make up the SARS-CoV-2 virus. These over-the-counter kits can be purchased at a local pharmacy and instructs you how to perform the test yourself. Results for these tests may come back in as little as 15 minutes.

Both of these tests can be useful, but it can be hard to know which is best for your particular circumstances.

Emily Spivak, MD, MHS, an associate professor of infectious diseases at University of Utah Health, offers the following information about how to test, when to test, and which test is best.

If you suspect you have COVID-19, should you get a PCR test or an antigen (rapid) test?

Ideally a PCR, because it's more sensitive and accurate, and more likely to detect the COVID-19 virus. If community transmission is high, it can take days to get a result. If this is the case in your area, a rapid home testing kit is useful during the symptomatic phase of illness, especially after 12 to 24 hours of symptoms.

If you've been exposed to COVID-19, on what day should you get tested?

The recommendation is three to five days after exposure. If you're symptomatic, sooner. If you've had a high-risk exposure and a rapid test comes back negative, it's best to follow up with a PCR test to truly rule out COVID-19 infection.

Is it safe to skip testing and simply assume you have the virus if you're experiencing symptoms?

It's always best to test, especially if you're at high risk of severe disease, work in health care, or interact with vulnerable populations. But if COVID-19 rates are high in your area, it's reasonable to assume you have COVID-19 if you have symptoms.

If you're sick—even if you don't have COVID-19—stay home. Whether it's COVID-19, the flu, or another infection, stay home and always wear a quality mask if you must go out in public

Are over-the-counter rapid tests as accurate in detecting COVID-19 as other methods?

Rapid tests are less sensitive than PCR tests, but they have a sensitivity rate of roughly 90% when people are symptomatic. They are less sensitive in asymptomatic individuals.

If you use a rapid test too early, less virus may be present and it could lead to a negative result. If you test early with symptoms and the result is negative but you suspect you have COVID-19, repeat the test 24-48 hours later or pursue PCR testing.

How accurate are PCR tests?

PCR tests are highly accurate, but they're not 100% accurate, and they're also subject to the accuracy of the sample that is collected. If you get a negative result but have symptoms of COVID-19 illness, isolate at home and repeat the test in 24 hours. Also, realize other respiratory viruses may be circulating in the community, and it is important to stay home to stop transmission of other viruses.

Do you need to test again if you had COVID-19 and are now symptom-free?

If you have a fever or significant cough after five days, stay home until your symptoms clear up. It's important to note that a cough may linger for days or weeks, so use discretion if your cough is productive and frequent. But if it's a dry, intermittent cough and your other symptoms have cleared, it's likely safe.