A Sensitive and Precise Radioimmunoassay for Human Thyroid-Stimulating Hormone

Abstract

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 × 10¹¹M⁻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 μU/tube. The mean normal hTSH value of 1.5 ± 1.0 μU/ml (mean ± sd) fell within the central one-third of the logit (B/B_o) 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.