PCR vs Ag tests for COVID-19
There are two types of COVID tests, a PCR test and an Antigen test.
PCR test:
| Measures genetic material from the virus | |
| Very sensitive | |
| Can detect genetic material and remain positive for 90 days even when virus particles are no longer alive or have potential to infect others |
Antigen (Ag) test:
| Detects protein on the surface of the vires | |
| Need enough virus present in the sample to pick up this protein to result in a positive test | |
| Usually reverts to negative in 5-14 days |
How well do antigen tests work?
In general, they may be able to catch most, but not all, cases of COVID-19 that are contagious at the time of the test. They are not as sensitive as PCR tests, which means that some people can have COVID-19 with a negative antigen test (i.e. a false negative). Antigen tests are more accurate when symptoms are present and may miss more than 50% of asymptomatic cases and 20% of symptomatic cases.
What are the best uses of antigen tests when I do not have any symptoms?
Antigen tests can play an important supportive role in preventing the spread of COVID-19. Note that a negative test result does NOT rule out infection, but it does make it less likely. If you donʼt have symptoms, it is still important to consider taking extra precautions such as masking while indoors when around people who could be at high risk of serious COVID-19 complications. When community transmission levels are high, a positive test likely indicates true infection and should be treated as such. Antigen tests can also be useful to try to detect early infection in those who have had a known close-contact exposure. A test taken 3-5 days after exposure will sometimes detect infection before symptoms are noticed.
What are the best uses of antigen tests when I do have symptoms?
If you have symptoms that could be due to COVID-19, an antigen test may be able to quickly confirm that you have infection. A positive test in that setting suggests that you have the infection and that you can pass it to others. You should treat a positive test as a true result. A negative antigen test does NOT rule out infection, you can book an appointment at Health Services to obtain a PCR test.
How can I obtain a COVID-19 Antigen test?
Antigen tests are available at most local pharmacies, including Quadrangle Pharmacy located within Health Services.
How can I obtain a COVID-19 PCR Test?
If your antigen test is negative and you are experiencing symptoms, PCR testing can be completed at Health Services on weekdays by appointment. Your student insurance is billed for this testing.
If you would like to use this service please email Health Services or call 314-935-4959 to arrange a test. Walk-in testing is not available.