Measurement of serum thyroxine by solid-phase chemiluminescence immunoassay

Descriptions are given of two solid-phase chemiluminescence immunoassays for the measurement of total thyroxine in serum. The antibodies were either attached to small uniform plastic microspheres (method 1) or passively adsorbed to antibody-coated tubes (method 2). The labelled antigen was thyroxine-aminobutyl ethyl isoluminol. After the antibody-binding reaction the antibody-bound fraction was washed, sodium hydroxide was added, and the mixture was incubated. Luminescence was initiated by oxidation of the label with microperoxidase/hydrogen peroxide and the signal integrated for 10 seconds. The light yield is inversely proportional to the concentration of thyroxine in the standard or sample. Both methods have similar sensitivity and precision to that obtained by a conventional radioimmunoassay.