Use of a cytochemical bioassay for determination of thyroid stimulating hormone in clinical investigation

Recently a highly sensitive cytochemical bioassay (CBA) for the determination of human TSH has been developed. The authors could show that this assay is specific for TSH and measurements done on plasma of normal euthyroid persons agree very well with radioimmunological findings. Because of the extreme sensitivity of the CBA it was possible to detect low but measurable TSH levels in patients with primary hyperthyroidism that were not increased by TRH treatment before therapeutic treatment. After therapeutic treatment, TRH application was able to stimulate additional biologically active TSH release which, however, barely reached the lowest limit of detection by RIA. In certain pathological cases it was possible to detect elevated plasma TSH levels which were active immunologically but inactive biologically. (author)