HEIA
HEIA formats are designed to be rapid and inexpensive, since the assays require no incubation or separation steps, and the reactions occur entirely in solution. The antigen being measured competes for a limited number of antibody binding sites with enzyme labeled antigen. The reagent antibody has the ability to block enzymatic activity when bound with the reagent enzyme-antigen complex preventing formation of product in the presence of substrate. The free antigen- enzyme complexes resulting from competition with measured antigen in the sample forms color-change products proportional to the concentration of antigen present in the specimen.