The Clinical Significance of Serum Triiodothyronine Measured by Radioimmunoassay in Various Thyroid Diseases

각종(各種) 갑상선질환(甲狀腺疾患)에서의 혈중(血中) $T_3$방사면역측정(放射免疫測定)의 진단적(診斷的) 의의(意義)

In an attempt to establish the diagnostic value of serum triiodothyronine and to correlate it with pathophysiologic mechanisms of thyroid hormones in various thyroid disorders, the author measured the serum triiodothyronine levels by means of radioimmunoassay and compared them with other thyroid function tests. This study was carried out in 152 cases with various thyroid functions; 28 cases as control, 51 cases of hyperthyroidism, 50 cases of euthyroidism and 23 cases of hypothyroidism. The results obtained were as follows: 1. The serum $T_3$ level in normal control group ranged between $131{\pm}34ng/dl$. 2. The serum $T_3$ levels ranged between $306{\pm}97ng/dl$ in hyperthyroidism $138{\pm}32ng/dl$ in euthyroidism and $60{\pm}27ng/dl$ in hypothyroidism. The significant differences between these groups were noted in this study. 3. In 5(9.9%) out of 51 cases with hyperthyoidism and 9(39.1%) of 23 cases with hypothyroidism, the serum $T_3$ were measured to be in normal range. Accordingly, the diagnostic value of the measurement of serum $T_3$ with hyperthyroidism was justifiable, but with hypothyroidism, it was less creditable than that of serum thyrotropin. 4. There was little significant difference between the diagnostic value of serum thyroxine and triiodthyronine levels in various thyroid disorders. However, $T_4/T_3$ ratio was decreased in patients with untreated hyperthyroidism because of more elevation of $T_3\;than\;T_4$. Consequently, the serum $T_3$ was more sensitive than $T_3$ in some thyroid disorders. 5. The serum $T_3$ level was much more sensitive and showed prompt shift in its level during the course of treatment on the patient with various thyroid disorders. And the measurement of serum $T_3$ was a good index for the evaluation of the thyroid function. From these results obtained, the measurement of serum $T_3$ by means of radioimmunoassay is a good way to understand the status of thyroid function with various thyroid disorders and evaluate the effects of the treatment given on these patients.