Examination of serum thyrotropic hormone level by 'supersensitive' immunoradiometric assay in functioning thyroid...

TSH determination by immunoradiometric assay (IRMA) has enabled the detection of subnormal levels of TSH and has thus opened up new vistas in the differentiation between euthyroidism and hyperthyroidism. The present investigations have proved that in patients with autonomous functioning thyroid adenoma with progressive clinical trend, when 'non-toxic' nodular goitre transforms into toxic adenoma, the basal serum TSH level is gradually decreasing. In case of a functioning thyroid adenoma detected by scintigraphy, the basal TSH concentration of the serum over 0.3 mU/l indicates euthyroidism. In preclinical hyperthyroidism, similarly to toxic adenoma, the serum thyroid hormone determination contributes to differentiating between the two clinical states. The IRMA for TSH determination makes it unnecessary, in the majority of cases, to perform the TRH (thyreotrop-releasing hormone) loading-test, which is needed only if the basal serum TSH level is in the borderline range, i.e. between 0.1 and 0.3 mU/l.