A sensitive and precise radioimmunoassay for human thyroid-stimulating hormone.

A high-sensitivity radioimmunoassay for human thyroid-stimulating hormone (hTSH) has been developed utilizing a highly specific rabbit antibody (developed by AFP) to hTSH with an affinity constant of 4.4 x 10(11) M-1. Optimal conditions which minimized both 125I-hTSH radiation damage and 125I dissociation included storage at -60 C in 0.25% albumin. Repetitive freezing and thawing did not cause loss of structural integrity or of full immunochemical reactivity of 125I-hTSH. Effects of human and calf sera on the precipitation of first antibody-bound 125I-hTSH by second antibody have been tabulated; the addition of TSH-free human serum to the standard curve is necessary to compensate for the serum effect. The minimum detectable amount of TSH in the new assay at a 1:1,000,000 final dilution of the hTSH antibody is 0.02 muU/tube. The mean normal hTSH value of 1.5 +/- 1.0 muU/ml (mean +/- SD) fell within the central one-third of the logit (B/Bo) plot where antigen concentrations are measured with highest precision. This assay gives good precision and reproducibility of measurements throughout the normal range of serum TSH concentrations.