English: Overview of enzyme-linked immunosorbent assay (ELISA)-based diagnostic test. ELISA can be presented in different formats based on differences in antigen immobilization and antibody labeling. In direct ELISA, SARS-CoV-2 antigen(s) bound to a plastic solid phase is detected by the addition of a conjugated antibody. In sandwich ELISA, the capture antibody is attached to the plastic solid phase. Antigen(s) in the sample will bind to the capture antibody and then be detected by a second enzyme-labeled antibody. In competitive ELISA, sample SARS-CoV-2 antigen is preincubated with the primary antibody and then added to a well coated with a secondary antibody along with an enzyme-conjugated antigen that competes with the sample antigen for binding with the primary antibody. The more SARS-CoV-2 antigen in the sample, the less conjugated antigen will be bound and the lower the signal will be.