Antigen and Antibody Tests: What's the Difference?


Mahshid Abir, Senior Policy Researcher

In the current COVID-19 pandemic, there are two tests that are being conducted to detect active infection with COVID-19 versus detecting antibodies in individuals who have had an infection and have recovered. These are very different tests conducted for different purposes, and they're both very important.

In the case of antigen testing, the test is being conducted on the individual where you're trying to see whether the person currently has active infection. In that case, if the test is positive for the antigen, that means that the virus is active in the person's body currently. Based on that test result, you give the person a recommendation for social distancing and quarantine so that they don't infect other people.

In the case of the antibody testing, you are testing people to see whether they've had the infection in the past. Antibodies are generated in our body during infection for various diseases, for bacteria and viruses. Typically, they persist in our body for a good length of time, and it differs based on the bacteria or virus after the infection has resolved. It is important to the antibody testing to get a good idea epidemiologically of how many people in the population actually have the infection.