[Oral TRH test: normal range and comparison with intravenous TRH test (author's transl)]

TRH (40 mg) was given orally to 122 patients with divers thyroid status. In euthyroidism, TRH induced TSH response ranged from 2.5 microU to 45 microU TSH, measured three hours after oral administration. TSH values were threefold higher following oral TRH (mean 24.5 microU) as compared to intravenous TRH-test using 200 microgram TRH (mean 7.05 microU). No exaggerated TSH response were found in patients on oral contraceptives and in euthyroid nodular goiter. Preclinical hypothyroidism was present in 50% in patients with previous partial thyroidectomy and only 15% of patients with blunted TSH response on an thyroid hormone regimen of 70 microgram thyroxine daily. Oral TRH test was negative in every patient with normal serum hormone levels under antithyroid drug therapy.