[Usefulness of the TRH-T3 test in the diagnosis of central hypothyroidism].
TRH tests (500 micrograms, i.v. bolus) were performed in 15 patients with various hypothalamic or pituitary disorders and in 6 control subjects. TSH (highly sensitive RIA) and T3 were measured before and 30, 60, 90 and 120 min. after TRH. In 8 out of 15 patients, low circulating thyroid hormone levels were observed, but their basal TSH levels were all in the normal range or even higher (0.8 - 5.5 microU/ml). Further, their integrated TSH responses (38 +/- 21 microU/ml) did not differ significantly from those of control group (35 +/- 16 microU/ml). Except for 2 cases with hypothalamic hypothyroidism, T3 increments after TRH were found consistently lower than 5 ng/dl in these hypothyroid patients. One of them revealed significant elevations of T3, T4 and thyroid 99mTc-pertechnetate uptake after 5 I.U. x 2 i.m. bovine TSH. In 19 cases studied (2 cases with hypothalamic hypothyroidism were omitted), basal T3 levels were found to show quite a good correlation (r = 0.738) with T3 increments after TRH. Therefore, TSH values by radioimmunoassay in hypothalamo-pituitary disorders were considered not relevant to be the levels of a real thyroid stimulator, or they seemed to contain biologically inactive moieties. In conclusion, measurement of the TSH level and even the TRH-TSH test were found unreliable in diagnosing central hypothyroidism, and the TRH-T3 test appeared to give quite useful diagnostic information.
D000293:Adolescent; D000328:Adult; D002648:Child; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D011863:Radioimmunoassay; D013972:Thyrotropin / Q000097:blood; D013973:Thyrotropin-Releasing Hormone; D014284:Triiodothyronine / Q000097:blood*
D014284:Triiodothyronine; D013973:Thyrotropin-Releasing Hormone; D013972:Thyrotropin