Usefulness of thyroglobulin antibody detected by ultrasensitive enzyme immunoassay: a good parameter for immune surveillance in healthy subjects and for prediction of post‐partum thyroid dysfunction

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Abstract
Using newly developed ultrasensitive enzyme immunoassay (EIA) for thyroglobulin antibody (TgAb), we have evaluated physiological and pathological implications of the antibody in healthy subjects as well as in autoimmune thyroid diseases.This EIA was based on the immune complex transfer method, and was 10(4)-fold more sensitive compared with the conventional haemagglutination assay (HA); the detection limit was 0.1 micrograms IgG/I, and the specificity of the assay was confirmed from the unequivocal decrease in the fluorescence intensity by the preincubation of test serum with Tg and/or inactive beta-D-galactosidase which blocks antibodies to the enzyme.TgAb was detectable in 159 (91%) of 175 healthy subjects aged 3rd to 7th decade (96 men and 79 women), and did not exhibit age or sex-associated change. In nine healthy women, the TgAb level significantly decreased as pregnancy progressed but increased transiently after delivery. TgAb was detectable in 52 (98%) of 53 patients with Graves' disease and all (100%) of 107 patients with chronic thyroiditis. Abnormal high TgAb values (> 40 micrograms/I), determined from the 95th percentile in healthy subjects, were shown in 40 (75%) with the former disease and 94 (88%) with the latter disease. Moreover, in 14 goitrous patients with biopsy-proved chronic thyroiditis with negative HA results, 12 (86%) showed abnormal high TgAb levels. In 69 patients with post-partum thyrotoxicosis in Graves' disease, 15 (79%) of 19 patients with the TgAb level of more than 2 x 10(3) micrograms/I in early pregnancy showed destructive thyrotoxicosis and 46 (92%) of 50 with less than this level showed stimulative thyrotoxicosis. This TgAb test could discriminate the two types of thyrotoxicosis more clearly than could the conventional TGHA test. In chronic thyroiditis, the mean TgAb value in early pregnancy was significantly higher in patients with postpartum hypothyroidism than in those without thyroid dysfunction. Hypothyroidism developed in 80% of the patients with a TgAb value of more than 10(3) micrograms/I.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.

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