Radioimmunoassay of human thyrotropin: analytical and clinical developments.

Recent modifications of the radioimmunoassay systems for TSH have greatly extended the clinical utility of the measurement of this hormone, so that its use is no longer limited to the diagnosis of primary hypothyroidism. The newer assays provide improved sensitivity and specificity, such that it is now possible to distinguish TSH levels that are within the normal range from those that are suppressed, e.g., in thyrotoxicosis. New vistas of clinical applications are being revealed as we improve our understanding of human thyroid physiology and pathophysiology. It is the purpose of this communication to summarize information about the improved TSH radioimmunoassay, to demonstrate the new observations available regarding TSH concentrations in various normal and diseased conditions, and finally, to illustrate the various ways in which the assay provides more accurate guidance in the clinical diagnosis and management of thyroid and nonthyroid disease.