Estimation of thyroxin, triiodothyronine, thyrotropin, free thyroxin, and triiodothyronine uptake by use of magnetic-particle solid phases.

We evaluated solid-phase radioassays involving small, uniform magnetic particles (MAGIC, Corning Medical), obtaining data on total serum thyroxin (T4), triiodothyronine (T3), thyrotropin (TSH), free thyroxin (FT4), and T3 uptake for a total of 301 serum samples from euthyroid patients; patients receiving replacement thyroxin; patients receiving estrogen, or who were pregnant; hyperthyroid, hypothyroid, and nonthyroidally ill patients; and patients receiving salicylates, phenytoin, or heparin. We found each procedure to be technically simple and precise (between-assay CVs for T4 2.8-8.2%, T3 9-7.4%, TSH 2.9-4.5%, FT4 3.6-11%, T3 uptake 2.2-3.7%). The magnetic separations are rapid (2 to 5 min), reproducible, and complete. Each MAGIC assay produced clinically appropriate results. These assay systems offer the convenience associated with noncentrifugation assays and excellent analytical performance.