U.S. Floats Doubling Up Antibody Tests to Improve Accuracy

(Bloomberg) -- In order to more accurately assess the spread of Covid-19, the U.S. should use multiple antibody tests at once, the White House recommended in a document issued Monday detailing the national strategy to expand testing efforts.

Tests that measure antibodies to SARS-CoV-2 rather than the virus itself will be crucial to understanding how widespread the outbreak really is -- and ultimately for rolling back restrictions on people and businesses. But such tests have been plagued by accuracy concerns as many have been rushed to market. In particular, antibody tests can be prone to false-positives, unwittingly identifying antibodies to other closely related viruses.

The White House acknowledged these issues in its report, suggesting the use of two antibody tests at the same time may solve the problem. The use of two tests would allow for the results to be checked against each other, in theory producing data that are more reliable.

“Highly specific and sensitive antibody tests will enable a better understanding of the spread of the virus and identify those who have already been infected,” the report said. “These tests, however, must be very accurate and reliable to guard against false positives, which can lead people to incorrectly believe they had the virus and may be immune from further infection.”

Antibody studies conducted so far have attracted ample criticism and varied wildly in their findings. A Stanford University study of Santa Clara County, California, concluded that more than twice as many people were infected with Covid-19 than current counts suggested, for a rate of infection of around 4%. A study by the state of New York found 21% of New York City residents had been exposed to the virus.

A high number of false-positives could mean the virus is not quite as widespread, but also more deadly.

Measuring signals that the body has encountered the virus in the past is more complicated than diagnosing the presence of the virus itself. Developing antibody tests requires more knowledge of a specific virus’s structure. In addition to tests potentially mistakenly identifying antibodies from other coronaviruses, different tests check for different antibodies, which can vary from person to person.

By comparing two tests to each other, the White House suggested, even if the same people tested positive for the virus on one test and negative on another, those results could be combined for a more accurate picture of the disease.

The U.S. Food and Drug Administration has thus far issued Emergency Use Authorizations to just eight antibody tests. The White House report recommended that labs independently validate others.

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