WASHINGTON (AP) Blood tests for the coronavirus could play a key role in deciding whether millions of Americans can safely return to work and school. But public health officials warn that the current Wild West of unregulated tests is creating confusion that could ultimately slow the path to recovery.

More than 70 companies have signed up to sell so-called antibody tests in recent weeks, according to U.S. regulators. Governments around the world hope that the rapid tests, which typically use a finger-prick of blood on a test strip, could soon ease public restrictions by identifying people who have previously had the virus and have developed some immunity to it.

But key questions remain: How accurate are the tests, how much protection is needed and how long will that protection last.

The blood tests are different from the nasal swab-based tests currently used to diagnose active COVID-19 infections. Instead, the tests look for blood proteins called antibodies, which the body produces days or weeks after fighting an infection. The same approach is used for HIV, hepatitis, Lyme disease, lupus and many other diseases.

Because of the relative simplicity of the technology, the Food and Drug Administration decided to waive initial review of the tests as part of its emergency response to the coronavirus outbreak.