Radioimmunoassay of human thyroglobulin with use of "thyroglobulin-free" plasma prepared by ultracentrifugation as diluent.

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Abstract
We describe the preparation and evaluation of a new diluent for use in preparing standard curves for the radioimmunoassay of human thyroglobulin (TG). This diluent, "TG-free human plasma, allows measurement of TG in lower concentrations than with previous assay systems because the components of the standards are more similar to those of the samples. TG-free plasma was prepared by a modification of the differential centrifugation method of Edelhoch (J. Biol. Chem. 235:1326, 1960). Standard curves prepared by use of TG-free plasma and plasma obtained from thyroidectomized patients were identical. In our assay, plasma from patients who had undergone total thyroidectomy produced no displacement when 25 to 100 microL of plasma was assayed. Twenty-five normal subjects all had detectable TG concentrations, ranging from 4.0 to 25.7 microgram/L. Only 27 of 2000 determinations performed by this new method had undetectable values and 26 of these were from patients with total or near-total thyroidectomies. TG concentration determined by this assay may be more sensitive for finding recurrent thyroid malignancy.