immunassay

Immunoassay is a type of biochemical test that measures the presence or concentration of a specific substance in a biological sample, such as blood, urine, or saliva. These tests rely on the highly specific binding reaction between an antigen and an antibody. An antigen is a molecule that can trigger an immune response, often a foreign substance like a virus or bacterium, or a specific protein. An antibody is a protein produced by the immune system to neutralize or identify the antigen.

In an immunoassay, either the antigen or the antibody is labeled with a detectable marker, such as an enzyme, fluorescent dye, or radioactive isotope. When the sample is introduced, the labeled component will bind to its corresponding target in the sample. The amount of bound labeled component is then measured, and this measurement is directly proportional to the amount of the target substance in the sample. Various immunoassay formats exist, including enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA), and chemiluminescent immunoassay (CLIA), each differing in the type of label and detection method used. Immunoassays are widely used in medical diagnostics for detecting diseases, monitoring drug levels, and pregnancy testing, as well as in research and food safety.