Sequential changes in serum thyroglobulin (Tg) and its autoantibodies (TgAb) following subtotal thyroidectomy of patients with preoperatively detectable TgAb

The changes in serum concentrations of thyroglobulin antibodies (TgAb) were investigated in eight patients with various thyroid disorders before, during and after thyroid surgery. TgAb was measured by a radioassay using 125I-thyroglobulin. In six patients the TgAb decreased rapidly during operation. Of these patients four had low concentrations pre-operatively, and the decrease in TgAb resulted in undetectable concentrations for more than 2 days, Serum thyroglobulin (Tg), measured in the specimens with undetectable TgAb, i.e immediately following surgery, showed concentration vs time curves resembling curves from patients with no antibody present. Furthermore, two of these patients had such a high concentration of TgAb pre-operatively that the initial Tg release was not sufficient to remove the TgAb, resulting in detectable TgAb throughout the investigation period. Serum samples drawn during and after operation were chromatographed according to molecular size, showing measureable Tg corresponding to 19S Tg. TgAb was only measureable in fractions corresponding to 7S IgG. The expected presence of complexed Tg and TgAb could not be demonstrated, but the analytical methods might have been unable to reveal this. The remaining two patients with thyroiditis showed no decrease in TgAb. This was compatible with a low content of Tg in the throid measured in one of them.

Quantitation of human serum antithyroglobulin antibodies by a two-site radioimmunoassay

A two-site solid-phase radioimmunoassay for measuring serum antithyroglobulin antibodies applicable to human serum is described. The sequential steps of the procedure include the adsorption of thyroglobulin (Tg) on polystyrene tubes and the binding of the antithyroglobulin antibody to solid phase followed by the fixation of labelled thyroglobulin. The optimal experimental conditions for the adsorption of unlabelled Tg, the uptake of the antibodies and the fixation of labelled Tg have been defined. The test is specific for antithyroglobulin antibody and its reproducibility and precision are satisfactory. The radioassay showed a good correlation with the hemagglutination method and, also, was found to be more sensitive. Levels of antithyroglobulin IgG in positive sera ranged from 0.3 microgram/ml to several mg/ml. In contrast to the double antibody radioimmunoassay for antithyroglobulin antibodies, this solid-phase radioassay is easier to perform; moreover, it is relatively independent of the quality, the purity and the specific activity of the tracer.