Radioimmunassay for measurement of triiodothyronine in human serum

Inder J. Chopra; David H. Solomon; Gildon N. Beall

doi:10.1172/JCI106696

Radioimmunassay for measurement of triiodothyronine in human serum

Inder J. Chopra, David H. Solomon, and Gildon N. Beall

Published October 1, 1971 - More info

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Abstract

A convenient, specific, precise, and reproducible radioimmunoassay system for measurement of triiodothyronine (T₃) in human serum has been developed. The procedure compares the ability of standards and unknowns to compete with radioactive T₃ for binding sites on a T₃-binding antiserum produced in rabbits by immunization with human thyroglobulin. The assay is set up in the presence of 250 ng thyroxine (T₄) in all tubes, to mobilize T₃ from its binding with the thyronine-binding globulin (TBG), and athyreotic sheep serum in standards to correct for the TBG in the unknowns. The method regularly detected 0.4 ng T₃, which would correspond to a T₃ concentration of 100 ng/100 ml when 400 μl of serum is analyzed. The mean recovery of unlabeled T₃ added to normal serum pools was 106%. Serial dilution of hyperthyroid sera containing high concentrations of T₃ with athyreotic sheep serum yielded expected values.

The serum T₃ concentration in 80% of 31 euthyroid normal subjects was less than 100 ng/100 ml (range < 100-170 ng/100 ml); it was greater than 170 ng/100 ml in 89% of 27 sera of hyperthyroid patients with untreated Graves' disease (range < 100-1300, mean 519 in 25 sera with detectable T₃). The concentration of serum T₃ fell, frequently to undetectable levels, during treatment of hyperthyroid patients with antithyroid drugs. The serum T₃ concentration in four hypothyroid patients was less than 100 ng/100 ml.