Antibody tests for the new coronavirus are capable of being incorrect roughly half of the time and should not be used to determine whether physical distancing or use of personal protective equipment is no longer necessary, the Centers for Disease Control and Prevention said.

These serologic tests, which test blood for antibodies created in response to the virus, SARS-CoV-2, should be used for research and virus surveillance purposes and not to make public health recommendations or to determine immunity, the federal health agency said in new interim guidance posted to its website.

If only a small percentage of those being tested are infected, the tests margin of error will be higher, whereas if the rate of infection is higher among those being tested, the positive predictive value increases, the CDC explained.