Covid-19 Antigen

How is a COVID-19 antigen test different from a PCR or molecular test?

While antigen and PCR tests detect signs of an active SARS-CoV-2 infection, there are important differences between them:

  • A PCR or molecular test looks for traces of the virus’s genetic material rather than for proteins found on the outside of the virus.
  • PCR can be performed on a sample taken from your nose, throat, or saliva, but antigen tests are currently only performed on samples from your nose or behind the nose.
  • While both are available as laboratory and site-of-care tests, antigen tests are most often used for site-of-care testing.
  • Antigen tests generally cost less than PCR tests.
  • PCR tests are generally considered more accurate and can be used to confirm the results of an antigen test.

How is a COVID-19 antigen test different from an antibody test?

Antigen and antibody tests have different purposes. Antigen tests look for an active infection, but antibody tests look for a past infection. Antigens are part of the virus, whereas an antibody is something that the immune system creates in response to exposure to a viral antigen. Antigen tests that look for the presence of the virus can detect an active infection, while antibodies, which develop a few weeks after viral exposure, test for a past infection. Another difference is that the antibody test uses a blood sample rather than a sample is taken from your upper respiratory tract.

What if I am interested in a COVID-19 diagnostic test or an antibody test?

You can contact your state or local health department or visit the department’s website for information on testing. If you have symptoms of COVID-19, contact your doctor to discuss your situation and find out how to prepare for your appointment before seeking a COVID-19 test in person.

Access to any of the tests depends on where you live, the availability of the test, and whether you find it eligible. In the US, collaborative efforts are underway to make more tests available. The national goal is to test more people as more tests become available.

How can diagnostic and antibody tests help reduce the spread of COVID-19?

With COVID-19 diagnostic tests, people who test positive and have symptoms can get care sooner. Contacts can be traced and self-isolation or quarantine can be started earlier to help stop the spread of the virus. But no COVID-19 test is 100% accurate. It is possible to test negative but actually be infected (false-negative result) or to test positive and not be infected (false-positive result).

Therefore, it is vital to continue to follow the COVID-19 guidelines from the Centers for Disease Control and Prevention, such as social distancing and wearing a mask when appropriate, until further notice. Antibody test results indicate how many people had COVID-19 and recovered, including those who had no symptoms. This helps determine who might have immunity, although it is not yet known to what extent and for how long.

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