Citing concerns about false positives, cross reactivity and uncertainty about the immune response to the virus, the AMA says serologic tests for the antibodies to SARS-CoV-2, the virus that causes COVID-19, should not be offered to individuals.
People who test positive for the protective antibodies may “falsely assume it is safe to discontinue physical distancing,” the AMA says in a statement issued yesterday. The physician’s organization also said that there is growing concern about poor test performance and fraudulent claims. And it cast doubt on the rigor of FDA approval process: “The FDA does not automatically independently verify performance of each of these tests and primarily relies on submitting manufacturers to self-validate their offerings.”
Serological tests should currently be used only in population studies, for evaluation of people who have recovered from COVID-19 who might be donating convalescent plasma, and in circumstances that are part of testing plan and “in concert with other clinical information,”
says the statement.
The AMA does not point to a specific false positive rate for the current crop of SARS-CoV-2 antibody tests. Rather, it makes a general point that even tests with high sensitivity and specificity will have false positives if the disease has a low prevalence “as is currently the case for COVID-19.”
While cross reactivity — a different infection, possibly with another type of coronavirus, producing antibodies that a serological test recognizes as being the same as those triggered by SARS-CoV-2 — has been a concern with some of current tests for SARS-CoV-2 antibodies. “For tests where cross-reactivity is possible, antibodies for other coronaviruses may result in a positive test result for SARS-CoV-2 even when the patient in question was not infected,” the AMA says.
The organization’s statement also mentions the uncertainty about the immune response to SARS-CoV-2. “It not yet clear when an immune response develops after COVID-19 infection, how strong this immune response may be, and how long the immune response may last,” says the statement.