High Quality Content by WIKIPEDIA articles! An immunoassay is a biochemical test that measures the presence or concentration of a macromolecule in a solution through the use of an antibody or immunoglobulin. The macromolecule detected by the immunoassay is often referred to as an "analyte" and is in many cases a protein. Analytes in biological liquids such as serum or urine are frequently measured using immunoassays for medical and research purposes.