Triiodothyronine production in Graves' hyperthyroidism.
OBJECTIVE
To quantify the relative contributions of thyroid secretion and peripheral generation to triiodothyronine (T(3)) production in untreated Graves' hyperthyroidism. PATIENTS, DESIGN, AND MEASUREMENTS: Thirty-one patients with hyperthyroidism, of whom 6 had T(3) toxicosis, and 21 surgically and radioiodine ablated patients with thyroid cancer on thyroid stimulating hormone-suppressive therapy in whom serum T(3) should reflect peripheral generation alone were compared with respect to serum free thyroxine (T(4)) and serum free T(3) concentrations.


RESULTS
Serum free T(4)/free T(3) molar ratios were virtually identical in the patients with T(4)+T(3) toxicosis (2.7 +/- 0.4) and those with T(3) toxicosis (2.6 +/- 0.4) and were significantly lower than in the patients with thyroid cancer (4.0 +/- 0.4) (p < 0.001). In the hyperthyroid patients, peripherally generated T(3) was calculated as the quotient of the individual serum free T(4) concentration and the free T(4)/free T(3) molar ratio in thyroid cancer; this value was subtracted from the individual measured free T(3) concentration to derive the value for secreted T3. Secreted T(3) accounted for 33 +/- 6% of T(3) production in T(4)+T(3) toxicosis and 34 +/- 10% in T(3) toxicosis.


CONCLUSIONS
This study indicates that about one third of T3 production in untreated Graves' hyperthyroidism, irrespective of whether presenting as T4+T3 toxicosis or T3 toxicosis, arises from thyroid secretion as compared to about 20% in normal individuals.
Woeber
Kenneth A
KA
University of California San Francisco, San Francisco, California 94143, USA. ken.woeber@ucsf.edu
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006111:Graves Disease / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013964:Thyroid Neoplasms / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood*
D014284:Triiodothyronine; D013974:Thyroxine