[The development of a sensitive radioimmunoassay for H-TSH and its clinical application (author's transl)].

Using a commercially available h-TSH RIA kit (Daiichi), a sensitive RIA method was developed. When pooled serum from patients with active Graves' disease was used as a carrier, combined applications of a delayed addition of 125-I TSH and utilization of X2 diluted anti-TSH antibody resulted in the consistent detection of 0.156 microunits/ml level of serum TSH. Further, 0.078 microunits/ml level could also be detected when 200 microliter of serum samples were applied. However, usage of 200 microliter sample volume should be determined after further studies concerning possible non specific effects of human serum. Assay results of 29 patient sera by the sensitive assay correlated quite well (r = 0.953, Y = 0.97X-0.06) with those by the regular assay. Serum TSH in all of the 20 normal subjects were detectable and ranged from 0.31 to 3.2 microunits/ml giving mean values of 1.48 +/- 0.65 (s.d.) microunits/ml. Values less than 0.156 microunits/ml were observed in patients with untreated Graves' disease, acute stage of subacute thyroiditis, and panhypopituitarism, and in postoperative cancer patients under suppressive doses of T-4. In conclusion, this sensitive TSH RIA made clear discrimination of low and normal serum TSH possible, and the clinical application of this method was considered quite useful.