Radioimmunoassay for Measurement of Thyroglobulin in Human Serum

Abstract

A specific and reproducible double antibody radioimmunoassay for the measurement of thyroglobulin (HTg) in human serum has been developed. Since antithyroglobulin autoantibodies combine with the [¹³¹I] HTg tracer, antibody-positive sera were rejected for measurement. Specificity is demonstrated in that thyroid analogous such as thyroxine (T₄), triiodothyronine (T₂) monoiodotyrosine (MIT) and diiodotyrosine (DIT) did not crossreact. Sera previously reacted with anti-HTg-Sepharose contained no immunoassayable HTg. Finally, sera obtained from patients after total thyroid ablation for thyroid carcinoma did not contain demonstrable HTg. The sensitivity of the assay is 1.6 ng/ml, and HTg was detectable in 74% of 95 normal subjects. The mean concentration was 5.1 ng/ml ±0.49 SEM (range P <0.01). A group of 17 thyrotoxic individuals all had elevated HTg levels; the mean for this group was 344.8 ng/ml ±90.7 SEM. In the acute phase of subacute thyroiditis HTg was also elevated in all of 12 patients, and the mean for this group was 136.8 ng/ml ±74.6 SEM.