New immunoenzymatic assay for human thyrotropin compared with two radioimmunoassays

We have evaluated a new immunoenzymatic assay for human thyrotropin involving three monoclonal antibodies (Abbott HTSH EIA) and compared the results with those of two conventional nonequilibrium double-antibody radioimmunoassay (RIA) methods: Clinical Assays' RIA and a research RIA (J Clin Endocrinol Metab 1975; 41:676). Mean values for thyrotropin in 100 euthyroid serum samples were similar in the Abbott and Clinical Assays methods, but both sets were significantly higher than those by the research RIA. By all methods, values for hypothyroid patients were clearly higher than values for euthyroid subjects. Results for hyperthyroid and euthyroid subjects were resolved slightly better with the research RIA than with the Abbott kit. The new Abbott assay was far more sensitive than either the Clinical Assays RIA or our research RIA. The correlation of results of the Abbott assay with those of the Clinical Assays and the research RIA exceeded 90% for samples from hypothyroid patients. The Abbott assay replaces radioisotope counting with spectrophotometric detection.