Using Antibody Tests for COVID-19
CDC has developed interim guidance for how healthcare providers, laboratories, and public health staff should use antibody tests. These tests look for the presence of antibodies, which are proteins made in response to infections. Antibodies are detected in the blood of people who are tested after infection; they show the body’s efforts to fight off a specific infection.
The virus that causes COVID-19 is new, and what we know about it changes rapidly. This guidance will be updated as more information becomes available.
- In general, a positive antibody test is presumed to mean a person has been infected with SARS-CoV-2, the virus that causes COVID-19, at some point in the past. It does not mean they are currently infected.
- Antibodies start developing within 1 to 3 weeks after infection.
- We currently don’t have enough information yet to say whether someone will definitely be immune and protected from reinfection if they have antibodies to the virus.
- Healthcare providers who use antibody tests must know how the different tests work and use caution when interpreting test results:
- If someone tests positive for SARS-CoV-2 antibodies but does not really have those specific antibodies, the result is a false positive. Similarly, if someone tests negative for SARS-CoV-2 antibodies but does really have those specific antibodies, the result is a false negative.
- FDA has authorized antibody tests for this virus that have been submitted for their review. But these tests are not 100% accurate and some false positive results or false negative results may occur.
- A higher percentage of positive results may be false positives when these tests are used in people who live or work in an area where very few people have had COVID-19.
- People who receive positive results on an antibody test but don’t have symptoms of COVID-19 or have not been around someone who may have COVID-19 are not likely to have a current infection. They can continue with normal activities, including work, but still take steps to protect themselves and others.
- People who receive positive results on an antibody test and who are currently or recently sick or have been around someone with COVID-19 should follow CDC recommendations on caring for themselves and protecting others, and when they can be around other people again.
- Until scientists get more data on whether antibodies protect against reinfection with this virus, everyone should continue to take steps to protect themselves and others, including staying at least 6 feet away from other people outside of their home (social distancing), even if they have had a positive antibody test.
- People who wear personal protective equipment (PPE) at work should continue to wear PPE, even if they test positive for antibodies to the virus.
- Antibody test results should not be used to determine if someone can return to work.
- Antibody test results should not be used to group people together in settings such as schools, dormitories, and correctional facilities.