Dozens of blood tests are rapidly coming on the market to identify people who have been exposed to the coronavirus by checking for antibodies against it. The Food and Drug Administration doesn’t set standards for these kinds of tests, but even those that meet the government’s informal standard may produce many false answers and provide false assurances. The imperfect results could be a big disappointment to people who are looking toward these tests to help them return to something resembling a normal life. First of all, it’s not clear whether someone who has antibodies to the coronavirus in their blood is actually immune. Your body produces these antibodies within about a week of infection. Another problem is that test results are wrong much more frequently than you might expect. While tests may truthfully say they are more than 90% accurate, in practical use they can often perform far below that level.