 Print page |
 Email page |
Triiodothyronine production by the thyroid is increased in patients with hyperthyroidism
The background of the study. The two thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are produced differently, in that all T4 but only 20 percent of T3 is produced by the thyroid; the reminder of the T3 is produced from T4 in other (extrathyroidal) tissues. The contribution of the two sources to T3 production may be altered in hyperthyroidism. In this study, the thyroidal and extrathyroidal contributions to T3 production were estimated from measurements of serum free T4 and free T3 in patients with hypothyroidism and patients with hypothyroidism treated with T4.
How the study was done. The study subjects were 25 patients with hyperthyroidism caused by Graves’ disease and 21 patients with thyroid carcinoma who were taking T4 (all had been treated with total thyroidectomy and radioactive iodine and were taking sufficient T4 to inhibit TSH secretion) (T4-therapy group). The contribution of extrathyroidal production of T3 to the serum free T3 concentration in the patients with hyperthyroidism was calculated based on the patient’s serum free T4 value and the serum free T4 and free T3 values in T4-therapy group. This calculated value represents the patient’s serum free T3 concentration if all the free T3 was produced by extrathyroidal production, as it is in the T4-therapy group. The difference between the patient’s measured serum free T3 value and this calculated value is the thyroidal contribution to the patient’s serum free T3 concentration.
The results of the study. The serum free T3 concentration attributable to extrathyroidal production of T3 in the patients with hyperthyroidism was 11.3 pmol/L (0.7 ng/dl). The concentration attributable to thyroidal secretion was 6.1 pmol/L (0.4 ng/dl), which amounted to 35 percent of the serum free T3 concentration in this group, considerably higher than in normal subjects.
The conclusions of the study. Approximately one third of serum T3 in patients with hyperthyroidism is produced by the thyroid, as compared with one fifth in normal subjects.
The original article. Woeber KA. Triiodothyronine production in Graves’ hyperthyroidism. Thyroid 2006;16:687-90.
Next Article: Activation of airport radiation sensors after radioactive iodine treatment in hyperthyroidism |
||
| Thyroid Digest Index | | | November 2006 Thyroid Digest |
