Antibody tests, often called serologic tests, look for evidence of an immune response to infection. “Antibodies in some persons can be detected within the first week of illness onset,” the CDC says.

They are not accurate enough to use to make important policy decisions, the CDC said.

“Serologic test results should not be used to make decisions about grouping persons residing in or being admitted to congregate settings, such as schools, dormitories, or correctional facilities,” the CDC says.

“Serologic test results should not be used to make decisions about returning persons to the workplace.”