Stimulation with thyrotrophin-releasing hormone (TRH) during antithyroid treatment

During antithyroid treatment a total of 88 TRH tests was performed in 56 clinical euthyroid patients. 56% had negative response to TRH (i.e. delta TSH smaller than 2 muU/ml) after being treated in average 12.6 months and no relation between the duration of treatment and the outcome of the TRH test was found. In the group with positive TRH tests (i.e. delta TSH greater than 2 muU/ml) the mean T4 value was slightly decreased (5.8 plus or minus SD 2.5 mug/100 ml) while the mean T3 value was normal (121 plus or minus SD 32 ng/100 ml). The group with negative TRH tests had quite normal serum T4 values (9.3 plus or minus SD 3.1 mug/100 ml) but in general high normal or elevated serum T3 values (175 plus or minus SD 31 ng/100 ml). Our results seem to indicate that serum T3 is of greater importance than serum T4 with regard to the outcome of the TRH test. The majority of the cases with negative TRH tests, however, had serum T3 and T4 values within normal range. In almost all patients with a negative TRH test a negative T3 suppression of 131I uptake in the thyroid gland was found while a positive TRH test was not correlated with suppressibility of 131I uptake.