(HealthDay)—The first COVID-19 virus antibody test for use in the United States has been approved by the Food and Drug Administration.

The test checks for protective antibodies in a finger prick of blood, revealing whether a patient has ever been exposed to COVID-19 and now may have some immunity, The New York Times reported. That is an important difference from current tests, which look for fragments of coronavirus genes that indicate an ongoing infection.

There are a number of reasons why the new is important. It may show that it is safe for people who are immune to COVID-19 to leave their homes and rejoin the workforce, and knowing whether they have COVID-19 may be especially crucial for , The Times reported. Also, antibody testing could provide a better idea of how widespread COVID-19 infection is in the population and improve calculation of the death rate. China, Singapore, and a few other countries already use COVID-19 antibody tests.

"If we don't know the asymptomatic or mild cases, we won't know if it's killing a sizable fraction of the people who have it, or only people who have underlying conditions or are very unlucky," Carl Bergstrom, M.D., an infectious disease specialist at the University of Washington in Seattle, told The Times.

As of Friday morning, there were 245,658 COVID-19 cases and more than 6,000 deaths reported in the United States, according to Johns Hopkins University.