Extended clinical utility of a sensitive and reliable radioimmunoassay of thyroid-stimulating hormone.

We have developed a radioimmunoassay for thyroid-stimulating hormone (TSH) that is sufficiently sensitive to permit reliable measurement of subnormal serum TSH levels. We report our evaluation of the utility of this radioimmunoassay in the diagnosis and management of thyroid disease. In 59 normal subjects, the mean serum TSH level was 1.49 +/- 0.10 microU/ml (mean +/- SEM) with the range 0.5 to 4.5 microU/ml. In patients without pituitary-hypothalamic lesions, the serum TSH level accurately reflected thyroid status, being subnormal in 29 hyperthyroid patients, supranormal in 26 hypothyroid patients, and normal in 31 euthyroid patients being treated for nonthyroid conditions. In patients being treated for either hyperthyroidism or hypothyroidism, the serum TSH level appeared to be a sensitive indicator of thyroid status, and its return to normal appeared to be a useful therapeutic criterion. We conclude that improving the sensitivtity and reliability of the serum TSH radioimmunoassay greatly extends its clinical applications.