Semi-automated radioimmunoassays for total serum thyroxine and triiodothyronine

Single stage semi-automated radioimmunoassays for total serum thyroxine (T4) and triiodothyronine (T3) are described which employ an automatic pipetting station, automatic gamma counter, and a programmable calculator with paper tape reader and printing facility. Both assays require only a small volume of unextracted serum, and are specific and sensitive. Their sample capacity, precision, speed, and cost are comparable with the measurement of serum protein-bound iodine. Both assays therefore have significant advantages over previous methods for the assessment of thyroid function in the diagnostic laboratory. A simple method of automating the calculation of results is described, which is applicable to any radioimmunoassay in which the standard curve is approximately linear on a plot of the free/bound fraction against the antigen concentration. In addition, a general method is reported which reveals the relative contributions of intrinsic, systematic, and random error to radio-immunoassay precision.