It consists in the detection of antibodies that produce the body’s defenses. Immunoglobulin m (IgM) is the first to appear in any infection. They occur approximately at seven days, so this type of diagnosis is not so effective at the beginning of infection.
In addition to IgM, the presence of another antibody, IgG against SARS-CoV-2, is also detected in a blood, serum or plasma sample.
In the case of the enzyme-linked immunosorbent assay (ELISA), it detects antibodies produced in the patient’s blood due to infection with SARS-CoV-2. To carry out the test, the biological sample is deposited together with the reagents (antibodies, antigens and enzymes) that from the produced reaction changes color.