Triiodothyronine radioimmunoassay and its application to thyroid disorders
Eisenstein, Z.; Boruchowsky, S.; Bank, H.; Czerniak, P.
Israel Journal of Medical Sciences 12(1): 1-10
1976
ISSN/ISBN: 0021-2180 PMID: 943381 Document Number: 106381
An accurate, sensitive triiodothyronine (T3) radioimmunoassay system is described. Direct measurement in serum is made possible by the use of T3-free serum for standards, and blocking of T3-binding of thyroxine(T4)-binding globulin with salicylate. T4 cross-activity was less than 0.3%. Mean T3 values in 55 euthyroid, 32 hyperthyroid and 19 primary hypothyroid patients were 1.46 plus or minus 0.17, 5.34 plus or minus 1.86 and 0.49 plus or minus 0.34 (s.d.) ng/ml, respectively. T3 was a more sensitive index than T4 in hyperthyroidism; in hypothyroidism it overlapped with euthyroidism. The presence of goitre had no effect on T3 concentrations in euthyroid patients. Among the patients studied, 8 had T3 toxicosis, including 2 with recurrent thyrotoxicosis. A significant rise in T3 was also found in euthyroid patients after thyroidectomy, whereas T3 remained normal. The extent of T4 and T3 increase was similar during the initial phase of subacute thyroiditis. There were lower T3 values and higher thyrotropin values in cord blood than in maternal blood. In 2 euthyroid subjects, thyroliberin stimulation caused a 50% rise in T3 and no change in T4 over a 2-h period.