Solid-phase radioimmunoassay of plasma triiodothyronine

A direct radioimmunoassay method for circulating triiodothyronine was set up, using an insolubilized (cellulose-coupled) antiserum and 8-anilino-1-naphthalene-sulfonic acid (ANS) as a protein inhibitor. Particular attention was paid to the evaluation of changes in the physico-chemical properties of the antibody sites under the experimental conditions adopted: no substantial decrease of immunoreactivity was found to be associated with the insolubilization process, while complex effects following the use of protein inhibitors were observed. The standardized procedure was defined in terms of analytical reliability both by a comparison with a reference (charcoal-dextran) method and by evaluation of sensitivity, precision and accuracy.