COVID-19 Antigen Test
About the Test
Antigen tests are a method of detecting an active infection with SARS-CoV-2, the coronavirus that causes the illness COVID-19. These tests look for antigens, which are protein markers found on the outside of a SARS-CoV-2 virus. The presence of these antigens is a sign of an active infection.
The test is performed on a sample that is taken by swabbing inside your nose. The sample can be analyzed on-site, providing results within about 15 minutes.
Purpose of the test
The role of antigen tests is to determine if a person has COVID-19. They are primarily used in screening for and in some cases diagnosing COVID-19:
Diagnosis is tested once a person has shown symptoms of a disease or has a known exposure to a disease.
Screening is looking for a disease in people who don’t have any signs or symptoms. Because antigen tests can be performed rapidly and at a relatively low cost, they may be used in large screening programs that involve repeatedly testing people to help prevent the spread of SARS-CoV-2.
There are various times when an antigen test for COVID-19 may be appropriate.
When you have been in close contact with someone who has COVID-19
When you have attended large social gatherings or otherwise been in places at high risk for virus transmission
When you either live or work in places where many people live together such as nursing homes, homeless shelters, or correctional facilities
When you need proof of a negative test to travel, work, or engage in other activities
Because antigen tests can deliver results quickly and cost less than PCR tests, they can be useful for screening programs. In these programs, people who test positive can be promptly isolated from others, but a second test with a PCR or other molecular test may be needed to confirm the diagnosis.
How is a COVID-19 antigen test different from a PCR?
While antigen and PCR tests both check for signs of an active SARS-CoV-2 infection, there are important differences between them:
A PCR test looks for traces of the virus’s genetic material instead of proteins found on the outside of the virus.
A PCR can be conducted on a sample taken from your nose, throat, or saliva, but antigen tests are performed on samples from your nose or behind the nose.
While both are available as both laboratory and point-of-care tests, antigen tests are more frequently used for point-of-care testing.
Antigen tests generally cost less than PCR tests.
PCR tests are considered to be more accurate and may be used to confirm the results of an antigen test.
See also: SARS-CoV-2 RNA (RT PCR COVID-19)
How is a COVID-19 antigen test different from an antibody test?
Antigen and antibody tests have different purposes. Antigen tests look for active infection, but antibody tests look for past infection.
Antigens are a part of the virus, while an antibody is something that the immune system creates in response to being exposed to a viral antigen. Antigen tests, which look for the presence of the virus, can test for active infection, while antibodies test for past infection.
Another difference is that antibody testing uses a blood sample instead of a sample is taken from your upper respiratory tract.