Discrepancy between the basal level of TSH and the thyrotropic response to TRH during thyroid hormone treatment of differentiated thyroid cancers

: Serum TSH (Thyroid Stimulating Hormone) was measured before and 30 minutes after a 200 microgram intravenous TRH (Protireline*) injection in 270 patients. These patients have been treated for one year at least, by a suppressive thyroid therapy after thyroidectomy for a differentiated thyroid carcinoma. 314 tests were performed. We used an ultrasensitive TSH method (Ciba-Corning-Diagnostics). The normal range (mean :1.68 mUI/l; range: 0.45 to 3.80 mUI/l) was determined in 116 euthyroid patients. Minimal response to TRH was studied in 35 untreated patients with hyperthyroidism (TSH TO: less than 0.30 mUI/l and delta TSH: less than 0.09 mUI/l). There was a relationship (r = 0.916) between TSH response 30 minutes after TRH stimulation (T30) and basal TSH value: in a logarithmic scale (fitting of the data by a bi-gaussian model). TRH tests were classified too, by basal TSH values (TO) and delta TSH (TSH at T30-TSH at TO). In 201 tests in which TO TSH was less than 0.30 mUI/l (maximal value in hyperthyroidism), 50 showed a delta TSH higher than 0.15 mUI/l (25% of the cases) and in 6 cases (3%), delta TSH was even higher than 2.0 mul/l; in 67 of the 75 tests (89.3%) where TSH TO is less than 0.15 mUI/l, delta TSH is no (less than 0.15 mUI/l). In 93 tests where TO TSH was upper than 0.45 mUI/l (minimal value in euthyroidism), delta TSH was higher than 2.0 mUI/l in 87 cases (93.6%).(ABSTRACT TRUNCATED AT 250 WORDS)