An antibody test looks for antibodies that are made by your immune system in response to a threat, such as a specific virus. Antibodies can help fight infections. Antibodies can take several days or weeks to develop after you have an infection and may stay in your blood for several weeks or more after recovery. Because of this, antibody tests should not be used to diagnose an active coronavirus infection. Antibodies do not mean that you are immune to the coronavirus in the future, but they are an important part of tracking the overall spread of the virus and whether you have had it in the past.