There are many good reasons to want an antibody test for SARS-CoV-2, the virus that causes COVID-19. But each of them comes with a lot of question marks. Determining if you have antibodies will confirm whether or not you were infected by the new coronavirus—but it won’t say how immune you’ll be to future attacks. Donating plasma may help patients who receive it—but researchers are still trying to find out whether it's an effective treatment. Lurking behind all these questions are the tests themselves: Who’s offering them, to whom, and how accurate they are has a lot of people scratching their heads.