A novel enzyme immunoassay (immune complex transfer enzyme immunoassay) for anti-thyroglobulin IgG using beta-D-galactosidase from Escherichia coli as label was reported previously. This immunoassay was highly sensitive in demonstrating anti-thyroglobulin IgG not only in all patients with Graves' disease and chronic thyroiditis but also in a large proportion of healthy subjects. However, the detection of anti-thyroglobulin IgG at low levels in some serum samples was difficult, probably due to the presence of anti-beta-D-galactosidase antibodies. In the present study, the use of inactive beta-D-galactosidase was tested for elimination of interference by anti-beta-D-galactosidase antibodies. Preincubation of serum samples with excess of inactive beta-D-galactosidase resulted in sufficiently low backgrounds to detect low levels of anti-thyroglobulin IgG with little effect on the dose-response of anti-thyroglobulin IgG. As a result, it was revealed that anti-thyroglobulin IgG was present in almost all healthy subjects as well as all patients with Graves' disease and chronic thyroiditis.

The ultrasensitive TgAb EIA was useful for detecting the physiological changes in autoantibody formation in healthy subjects and the TgAb value was useful for predicting post-partum thyroid dysfunction in autoimmune thyroid diseases. This EIA is useful for the evaluation of the immune surveillance in patients with autoimmune thyroid diseases as well as in healthy subjects.