[Intrinsic value of a radioimmunologic TSH assay]

TSH-measurements in plasma as a single parameter for the evaluation of thyroid status need a highly sensitive radioimmunoassay, hitherto not available from commercial sources. The results, however, of such an assay allow to distinguish satisfactorily between suppressed, partially suppressed and normal regulation as well as overstimulation of the thyroid. For several indications, the TRH-test could be replaced by a basal TSH-value. Suppressed regulation without measurable TSH-levels is not to be identified automatically with clearcut hyperthyroidism because of several disturbing factors to be considered in clinical circumstances. Normally the positive TRH-test includes basal TSH-levels between 0.5 and 5 microunits/ml thereby excluding significant hormone excess as a possible cause of clinical signs of hyperthyroidism; however, some exceptions do exist (TSH-secreting pineal tumors; partial TSH-resistance of the hypophysis; crossreacting immunoglobulins after microbial vaccination) and should be considered in case of conflicting results. From a clinical point of view a highly sensitive TSH-RIA would be very interesting but would require the use of most recent technologies.