Radioimmunoassay for measurement of thyroglobulin in human serum

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 [(131)I] HTg tracer, antibody-positive sera were rejected for measurement. Specificity is demonstrated in that thyroid analogous such as thyroxine (T(4)), triiodothyronine (T(2)) 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 <1.6-20.7 ng/ml). Day to day variation in HTg levels is large in some euthyroid subjects and nearly absent in others. HTg was detectable in 90% of the sera obtained in 23 pregnant women at delivery in whom a mean concentration of 10.1 ng/ml +/-1.3 SEM was observed. The mean level for the corresponding newborn infants at birth was 29.3 ng/ml +/-4.7 SEM a value significantly higher than the mean maternal HTg concentration (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.