This week, the U.S. government approved the first blood test in the country that will look for the antibodies produced by the body to fight the novel coronavirus. Such a test can reveal whether someone is actively infected by the virus, as well as whether they were previously infected but recovered. While these tests are very much needed to better understand the scale of the outbreak, they have a few major limitations.

On Thursday, the Food and Drug Administration issued an Emergency Use Authorization to a covid-19 antibody test developed by the company Cellex. The test looks for two types of antibodies, IgM and IgG, created by the body’s immune system in response to the new coronavirus, known as SARS-CoV-2. The test, which requires blood drawn from a vein, can return results within 15 to 20 minutes, though the testing itself has to be done in a certified laboratory, not at a doctor’s office, unlike some other rapid covid-19 tests.