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COVID19 Antibody Tests

More than 15 companies have notified the U.S. Food and Drug Administration that they have developed antibody tests. These companies are permitted to begin distributing the tests to hospitals and doctors’ offices, provided they include a disclaimer stating that, “This test has not been reviewed by the FDA.” These serology tests will not play an important role in the diagnosis of acute infections. Preliminary studies indicate that IgM antibody does not become detectable until one to two weeks after the onset of symptoms. A negative serologic test might give patients a false sense of assurance that they are not infected and cause them to ignore healthcare instructions to shelter in place and maintain social distancing.

Sensitivity is approximately 75%. The spike protein is the most immunogenic portion of the virus. It shares much homology with other coronaviruses. Insufficient data is available to determine cross-reactivity or the false positive rate.

Antibody tests will be valuable for:

  • Epidemiologic studies to determine the extent of community spread
  • Determination if immunity develops and its duration
  • Assessing immunity to allow people and health care workers to return to work
  • Recruitment of recovered patients to donate convalescent plasma

COVID19 antibody tests should not be used for diagnosis of COVID19 infection but will be useful for assessing community spread and immune status. 


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