Standardization of TSH Testing

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Abstract
A comparison of various dosage regimens of thyrotropin has been made to determine which gives the most effective stimulation for the clinical evaluation of thyroid function. The lowest dose used, one injection of 5 USP units, gave a maximal response of the 131I uptake in euthyroid patients, but not in those with hypothyroidism secondary to pituitary disease. In the latter, 3 injections of 5 U each at 24-hr intervals gave maximal stimulation of the 131I uptake. Three patients with long-standing Sheehan's syndrome showed no response, although 1 of the 3 had shown a marked response to her initial TSH test 8 years before and 2 other patients had shown clear responses on initial testing. In hypopituitary patients on treatment the serum protein-bound iodine concentration appeared not to give a reliable estimate of the thyroid's capacity to respond to thyrotropin. It is concluded that 3 injections of 5 USP units given at 24-hr intervals, with measurement of the thyroidal 24-hr 131I uptake 42 hr after the final dose, is the optimal procedure. The mean final value for the 131I uptake in the euthyroid patients following 5 U of TSH 3 times was 41 (±16) % (mean and standard deviation), and was 32 (±10) % in the panhypopituitary patients, excluding those with Sheehan's syndrome.