Improved radioimmunoassay for human TSH

This study concerns the optimization of the human TSH (h-TSH) radioimmunoassay with special emphasis on reducing the heterogeneity of the 125I h-TSH tracer. Enzymatic iodination of h-TSH with glucose oxidase/lactoperoxidase was shown to be superior to either low or high dose chloramine-T procedures, producing a high specific activity reagent (70-150 μCi/μg) with minimal evidence of damage. Tracer purification procedures not only affected initial immunoactivity but also storage stability and heterogeneity of the resulting 125I h-TSH. The assay developed using these technical approaches shows a sensitivity limit of 0.005+-0.001 (S.E.M.) μU/tube; 50% displacement at 0.18+-0.08 (S.E.M.) μU/tube and complete delineation between euthyroid (n=49, 2.44+-0.18 (S.E.M.) mU/l, range 1.00-6.08) and hyperthyroid (n=62, 0.34+-0.02 (S.E.M.) mU/l, range 0.10-0.85), serum h-TSH levels. (Auth.)