A fully automated solid-phase radioimmunoassay for triiodothyronine.

We report the first solid-phase radioimmunoassay for triiodothyronine with use of antibody-coated tubes, which is designed specifically for the fully automated radioimmunoassay instrument, Micromedic Systems' "Concept 4 Automatic Radioassay." Antisera to triiodothyropropionic acid/bovine serum albumin were raised in rabbits, purified by ammonium sulfate precipitation, and coated onto polypropylene tubes. Analytical recovery of exogenous triiodothyronine added to sera from normal men and women and pregnant women was quantitative. Intra-assay and inter-assay coefficients of variation are 4-5 and 6-9%, respectively. Correlation coefficients (r) for comparison of sample values with those obtained by three commercial laboratories were 0.95, 0.84, and 0.91. The sensitivity of the assay is 0.5 microng/liter. The assay can be performed either manually or be fully automated on the "Concept 4."

An 125I-labeled cortisol radioimmunoassay in which serum binding protein are enzymatically denatured.

We report an iodine-125 radioimmunoassay for cortisol in biological fluids, in which interfering binding proteins are enzymatically denatured. An antiserum to cortisol-3-carboxymethyloxime-bovine serum albumin, extremely low cross-reacting with other corticosteroids, was raised in rabbits. A cortisol-3-carboxymethyloxime tyrosine methyl ester derivative was synthesized and labeled with iodine-125 by standard radioiodination techniques. To eliminate the need for extraction and recovery procedures, we digested interfering binding witha proteolytic enzyme, which then was heat-inactivated before adding the labeled derivative and the premixed, preincubated antiserum complex. There was quantitative analytical recovery of esogenous cortisol added to sera from a normal man, a normal woman, and a pregnant woman. Values for the same samples agreed after extraction and chromatographic purification and agreed well with values obtained by other techniques by independent reference laboratories. The five-step assay can be done in 6 h or less.