A new monoclonal-antibody two-site solid-phase immunoradiometric assay for human thyrotropin evaluated.

We compared results with a commercial solid-phase two-site immunoradiometric assay kit for human thyrotropin in which monoclonal antibodies are used (TANDEM-R TSH; Hybritech Inc.) with those by our radioimmunoassay (J Clin Endocrinol Metab 41:676, 1975), which is optimized for measurement of low concentrations of thyrotropin. In the immunoradiometric assay a specific antibody to the beta subunit of human thyrotropin is immobilized on a polystyrene bead, and a radiolabeled monoclonal antibody directed against the alpha subunit provides a measure of bead-immobilized hormone. The mean thyrotropin concentrations in 70 euthyroid serum samples were similar in the two assays. Values for hypothyroid patients were clearly higher in both assays than values for euthyroid individuals. In commercial assays the major source of error in measurement of thyrotropin response to thyroliberin in terms of the increment over the basal concentration of thyrotropin has been systematic errors in the measurement of those basal concentrations. With the present assay, however, basal values are obtained with good precision and accuracy: CV = 2.9% at 6 milli-int. units/L (n = 48).