The FDA authorized its first serology tests designed to estimate the numbers of coronavirus antibodies in a person’s bloodstream, instead of simply providing a positive or negative result on whether they are present.
While it is still not known how long COVID-19 antibodies linger following an infection—or what levels may be necessary to provide protective immunity, and in what way—these tests can be used to identify people with a strong immune system response to the virus.
Since early April, the FDA has officially greenlit 33 antibody tests, all of which are designed to provide a simple yes-or-no. The two latest diagnostics are new versions of previous assays developed by Siemens Healthineers, under the company’s Atellica and ADVIA Centaur labels, which were first authorized by the agency in late May as total antibody tests.
They provide what the company and the FDA describe as “semi-quantitative” readings of IgG antibodies, giving an estimate of their number instead of a precise measurement. IgG antibodies typically appear in the blood in the weeks after symptoms begin to show, and can be found much longer after an infection compared to other types of antibodies detected by previous tests.
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Both of Siemens’ fully automated tests are chemiluminescent immunoassays, which tag coronavirus antibodies with reagent markers that produce light through a chemical reaction. When more antibodies are present in a sample, more light is produced.
“Being able to measure a patient’s relative level of antibodies in response to a previous SARS-CoV-2 infection may be useful as we continue to learn more about the virus and what the existence of antibodies may mean,” said Tim Stenzel, director of the FDA’s Office of In Vitro Diagnostics and Radiological Health.
“There are still many unknowns about what the presence of SARS-CoV-2 antibodies may tell us about potential immunity, but today’s authorizations give us additional tools to evaluate those antibodies as we continue to research and study this virus,” Stenzel added. “Patients should not interpret results as telling them they are immune, or have any level of immunity, from the virus.”
In addition, the agency said results from these tests should not be taken as a sign that a person could stop following social distancing procedures or forgo wearing a mask, and that they do not detect active or asymptomatic COVID-19 infections.