In the guidelines, CDC recommends that antibody tests not be used, at this time, to make policy decisions or to determine if an individual has immunity to
On May 26, 2020, the Centers for Disease Control and Prevention (CDC) issued interim guidelines for COVID-19 antibody testing in clinical and public health laboratories. The guidelines contain recommendations for clinical and public health laboratories regarding: 1) choice of test and testing strategy; 2) individuals who test positive for COVID-19 antibodies; and 3) additional considerations on the use of antibody tests.
In the guidelines, CDC recommends that antibody tests not be used, at this time, to make policy decisions or to determine if an individual has immunity to COVID-19. Over time, these tests should be able to help determine the proportion of a population previously infected with COVID-19 and provide information about populations that may have certain levels of immunity and potentially be protected.
Choice of Test and Testing Strategy
The guidelines recommend antibody tests that have Emergency Use Authorization for public health or clinical use since their test performance data have been reviewed by the FDA. Positive predictive value should be optimized in deciding to use any specific antibody test. By way of example, tests can be optimized, particularly if results are returned to individuals, in the following ways:
- Choosing a test with a very high specificity, perhaps 99.5 percent or greater, will yield a high positive predictive value in populations tested with antibody-positive prevalence of 5 percent or greater;
- Testing persons or populations with a high pre-test probability of having antibodies (e.g., persons with a history of symptoms compatible with COVID-19 or who are exposed to areas or institutions experiencing outbreaks); or
- If a high positive predictive value cannot be assured with a single test, use of an orthogonal testing algorithm (see, e.g., Table 1 from the guidance) in which persons who initially test positive are tested with a second test.
The CDC is advising that antibody tests should be used in patients who present nine to 14 days after the onset of symptoms and in people who may have late complications associated with COVID-19.
Individuals Who Test Positive for COVID-19 Antibodies
The guidelines indicate that individuals who have tested positive for COVID-19 antibodies are not necessarily protected from future infection until the durability and duration of immunity is established. Individuals who have tested positive for COVID-19 antibodies should follow general recommendations to prevent infection and otherwise continue with normal activities, including work. Further, the CDC recommends that there should be no change in clinical practice or use of personal protective equipment by healthcare workers and first responders who test positive for the COVID-19 antibody.
Antibody Tests Not Predictive for Return-to-Work Decisions
The guidelines indicate that antibody tests should not be used to make decisions about persons returning to work or grouping persons residing in or being admitted to congregate settings, such as schools, dormitories or correctional facilities. At the present time, the positive predictive value of antibody tests is not sufficient to justify making policy decisions based on results of antibody tests for a single individual. Testing for IgA antibodies is not recommended (as opposed to IgM or IgG antibodies). Further, based on the present tests and information, there is no distinction between antibody tests for IgG, IgM or total antibody tests.
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