Final answer:
A competitive EIA is an enzyme immunoassay commonly used to detect and quantify antigens in medical diagnostics and research. The antigen competes with a labeled antigen for binding to a limited amount of antibody, and the bound labeled antigen is indirectly proportional to the concentration of the target antigen in the sample.
Step-by-step explanation:
Enzyme immunoassays (EIAS) are a type of assay used to detect and quantify antigens. In a competitive EIA, the antigen competes with a labeled antigen for binding to a limited amount of antibody. The amount of labeled antigen that is bound to the antibody is indirectly proportional to the concentration of the target antigen in the sample. This type of EIA is commonly used in medical diagnostics and research to measure hormone levels, drug concentrations, and the presence of infectious agents.