Both PCR and antigen testing are intended to diagnose active COVID-19 infections, using saliva or a nasal swab.  While an individual has an active infection, both PCR and antigen test will be positive. Once an individual has recovered, both the PCR and antigen test will be negative.  Antibody tests do not detect active infection. Instead, they are designed to detect an immune response to a past exposure to COVID-19. Antibody tests conducted too early following an infection (<7 days) will read negative. Once an individual develops an immune response, the antibody test will read positive.