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."