Which immunoassay method for thyroxine uses chemiluminescence to emit light from a chemical reaction?

• A. Fluorescent polarization immunoassay (FPIA)
• B. Chemiluminescence
• C. Fluorescent substrate-labeled inhibition immunoassay
• D. Microparticle enzyme immunoassay (MEIA)

Answer: (B)

Chemiluminescent immunoassay uses light emitted from a chemical reaction to quantify thyroxine. In this approach, a chemiluminescent label is attached to the antibody or antigen, and after binding and washing, a substrate triggers a light-producing reaction. The emitted light is measured by a luminometer, with signal strength proportional to the thyroxine concentration, enabling high sensitivity and wide dynamic range. Other approaches rely on fluorescence or enzyme-generated color signals rather than light from a chemical reaction, so they don’t use chemiluminescence as the detection mechanism.