Published January 20, 2022

At-home rapid antigen tests are becoming more widely available through state and federal programs.  These tests can be useful tools as part of a multi-layered strategy to reduce community transmission; however, they also have important limitations.  They can provide some extra reassurance to asymptomatic people who must be in an indoor unmasked setting, and they can be used to identify COVID-19 in people with symptoms when they have a positive test result.  But, these tests can be less helpful when they are negative, especially when there is a lot of COVID circulating in the community (like now). In people who have COVID and symptoms, rapid antigen tests can be negative up to 20% of the time. For this reason, if you have symptoms, a negative rapid antigen test cannot assure you that you do not have COVID and you cannot come to work or school with a negative rapid antigen test if you have symptoms.  You must get a PCR test.  Additional details can be found in these FAQs.


Are rapid at-home antigen tests available?  Free FDA-authorized rapid antigen tests are becoming available through a number of places, including from the federal government, the Missouri state health department; and supply is gradually increasing in retail pharmacies.  How do antigen tests work?  These tests directly detect the presence of the COVID-19 virus from a swab taken from the nose.  

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 (ie 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.  

Do antigen tests work for Omicron?  Antigen tests that are authorized by the FDA for emergency use do detect the Omicron variant, however some studies suggest that the sensitivity to detect this variant may be lower, meaning there may be more false negatives.  

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.  If you are planning to get together with friends or family, and you don’t have any symptoms, a negative test can provide some extra reassurance that, at that moment, you do not have COVID-19 that can be passed to them.  Note that a negative test result does NOT rule out infection, but it does make it less likely.  If you have symptoms, you should not attend any gathering until you have had a PCR test. If you don;t 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 and stay home while contacting Student or Occupational Health.  A negative antigen test does NOT rule out infection, and you must be tested with the more sensitive PCR test before returning to work or school.  

When should I not use an antigen test?  A negative antigen test result cannot be used to determine if it is safe to come to school or work when symptoms are present.