Human Serum Thyrotrophin Measurement by Ultrasensitive Immunoradiometric Assay as a First‐line Test in the Evaluation of Thyroid Function

Abstract

An ultrasensitive immunoradiometric assay (IRMA) using two monoclonal anti-TSH antibodies has been used for TSH measurements in basal conditions and after TRH stimulation. The results have been compared with those obtained by conventional radioimmunoassay (RIA). The IRMA method had very high sensitivity (0.07 microU/ml). Detectable serum TSH concentrations were found in all normal subjects by IRMA, but in only 76% by RIA. No overlap was observed with the results obtained by IRMA in untreated overtly hyperthyroid patients, in whom serum TSH was below the limit of detection. The relationship between basal and TRH-stimulated serum TSH concentrations by IRMA and RIA was evaluated in 176 subjects including normals and patients with untreated and treated hyperthyroidism, functioning thyroid adenoma, nontoxic goitre and patients on L-thyroxine therapy. A normal TSH response to TRH was observed in virtually all patients with detectable basal serum TSH by both methods. When patients with undetectable basal serum TSH levels were considered, all but one (98%) had no TSH response to TRH by IRMA. On the contrary using RIA, an absent response was found only in 47% of subjects, a blunted responses in 10% and a normal response in 42%. These data indicate that basal serum TSH measurements by IRMA allows a complete discrimination of normal from hyperthyroid patients and can avoid the need for TRH stimulation tests.

Clinical Usefulness and Limitations of Serum Thyrotropin Measurement by ‘Ultrasensitive’ Methods

“…How ever, the finding that almost 20% of the patients presenting with nontoxic goiter and clinically euthyroid on all grounds showed an equivocal TSH level suggests that the absence of complete discrimination between euthyroid and hyperthyroid patients could be accounted for by the pathophysiological conditions of the patients. Our results, taken together with those published by other au thors [11,13], do not allow to clearly distin guish the five kits used in this study. The choice of a kit would thus be the result of compromise between procedure and perfor mances.…”

“…These assays, however, were cum bersome, time-consuming and often expen sive, so that they could not be employed on a routine basis. Immunometric assays based completely or partially upon monoclonal anti-TSH antibodies have now been devel oped by a dozen or more companies [5][6][7][8][9][10][11][12][13], These commercially available TSH ultrasen sitive assay kits would open a new era in thy roid diagnosis and follow-up as far as they satisfy the claim that they allow simple, rapid and precise determination of TSH con centrations substantially lower than normal, and completely discriminate hyperthyroid from euthyroid subjects. The analysis of the data presented here and in other reports [11,12], clearly shows that none of the kits al ready on the market completely distin guishes normal subjects from thyrotoxic pa tients.…”

“…Recently, new immunometric assays based completely or partly upon monoclonal antibodies have opened the possibility to routinely assay TSH concentration in hyperthyroid patients [5][6][7][8][9][10][11][12][13]. In a previous report, we have compared the results of TSH deter mination by a conventional radioimmuno assay to those obtained by an ultrasensitive immunoradiometric assay [13].…”

“…In a previous report, we have compared the results of TSH deter mination by a conventional radioimmuno assay to those obtained by an ultrasensitive immunoradiometric assay [13]. In this re port we used five different ultrasensitive TSH assay kits with the aim to further delin eate the clinical usefulness and limitations of serum TSH measurement by ultrasensitive methods.…”

Optimum Replacement Dose of Thyroid Hormone Assesed by Highly Sensitive TSH Determination in Patients with Congenital Hypothyroidism.

“…Therefore, our data for children supported this suggestion as in adult patients. Recently, a highly sensitive assay for TSH has been developed (Seth et al, 1984;Caldwell et al, 1985;McBride et al, 1985;Martino et al, 1986;Sato et al, 1987a.) Therefore, we divided the IRMA-TSH concentrations into four groups and studied the correlations of serum thyroid hormone concentrations among them in the present study.…”