The US Centers for Disease Control and Prevention said that antibody tests used to determine if people have already been infected with COVID-19 in the past might be wrong up to half the time.
Antibody tests or serologic tests are tests that look for evidence of an immune response to infection. In some persons, antibodies can be detected within the first week of illness onset. However, the tests are not reliable enough to base important decisions on.
The CDC sais that antibodies test results should not be used to decide about grouping people residing in or being admitted to gatherings such as schools, dormitories, or facilities such as jails. Serologic tests mustn't be used to decide whether people can return to their workplace.
Health officials or health care providers who are using antibody tests need to use the most accurate test they can find and might need to test people twice.
The falseness of the antibodies test has to do with how common is the virus among the tested population. “For example, in a population where the prevalence is 5%, a test with 90% sensitivity and 95% specificity will yield a positive predictive value of 49%. In other words, less than half of those testing positive will truly have antibodies,” the CDC said.
