In hyperthyroidism, the TSH response to TRH is suppressed. Absent response to TRH may also be found in certain patients with nodular goitre and in patients with ophthalmic Graves' disease who are borderline toxic. An absent TSH response is thus consistent with, but not diagnostic of, hyperthyroidism. A normal TSH response to TRH excludes hyperthyroidism (except that due to TSH adenoma or pituitary T4 resistance). Thyroid autonomy may result in a flat TSH response to TRH, but correlation with the T3 suppression test is not as close as might be expected, perhaps because the two tests measure different aspects of the thyroidΓÇôpituitary axis.
