Principles of immunochemical techniques used in clinical laboratories

Immunochemistry offers simple, rapid, robust yet sensitive, and easily automated methods for routine analyses in clinical laboratories. Immunoassays are based on highly specific binding between an antigen and an antibody. An epitope (immunodeterminant region) on the antigen surface is recognized by the antibody's binding site. The type of antibody and its affinity and avidity for the antigen determines assay sensitivity and specificity. Depending on the assay format, immunoassays can be qualitative or quantitative. They can be used for the detection of antibodies or antigens specific for bacterial, viral, and parasitic diseases as well as for the diagnosis of autoimmune diseases. Immunoassays can measure low levels of disease biomarkers and therapeutic or illicit drugs in patient's blood, serum, plasma, urine, or saliva. Immunostaining is an example of an immunochemical technique, which combined with fluorescent labels allows direct visualization of target cells and cell structures.