(FIA) A fluorescent immunoassay (also called fluoroimmunoassay) is an analytic assay method based on a fluorescent-labeled antigen or antibody. Fluorescent measurements are usually more sensitive than spectrophotometric measurements. Therefore, FIA methods have greater analytical sensitivity than enzyme immunoassay techniques.

(EIA) Enzyme immunoassays have been developed as an alternative to radioimmunoassays. These methods use an enzyme to label either the antibody or antigen. The sensitivity of an enzyme immunoassay is similar to that for a radioimmunoassay, without the danger of radiation. One of the most widely used EIA for detection of infectious diseases is the ELISA (Enzyme Linked lmmuno Sorbent Assay) method.

See also Fluorescent Immunoassay.

(RIA) A radioimmunoassay is an in vitro assay test in which very small quantities of hormones, drugs and other substances in blood, urine, etc. can be measured by using specific antibodies or antigens which have been labeled with radioactive tracers. Since the patient does not receive the radioactive material, there is no patient radiation exposure.
Radioimmunoassays are usually replaced by fluoroimmunoassay and enzymimmunoassay to avoid the use of radioactive materials.

See also Bioassay, Fluorescent Immunoassay, Protein Binding Assay, Radioassay, and Berson Salomon.