Immunological assays are a biochemical test that measures the presence or concentration of a macromolecule or a small molecule in a solution through the use of an antibody or an antigen. Immunological assays come in many different formats and variations, and may be run in multiple steps with reagents being added and washed away or separated at different points in the assay. Enzymes are popularly used in these immunological assays to track antibodies and antigens.