Study on Enzyme Immunoassays for the Measurement of Thyroglobulin and Anti-Thyroglobulin Autoantibody in Human Serum

Enzyme-linked sandwich immunoassays for the measurement of thyroglobulin and anti-thyroglobulin autoantibody in human serum using silicone rod and beta-D-galactosidase were studied. These methods showed excellent results in specificity, sensitivity, precision and clinical application. 1) A method using silicone rod coated with rabbit (anti-human thyroglobulin) immunoglobulin G and rabbit (anti-human thyroglobulin) monovalent fragment of immunoglobulin G (Fab') conjugated with beta-D-galactosidase was developed for the measurement of circulating thyroglobulin. The sensitivity of the assay with as little as 2 microliter of serum was 10.7 amoles/tube corresponding to 3.5 ng/ml of serum, which was equal to or rather higher than that of radioimmunoassay. The correlation coefficient between values determined by the present assay and a double-antibody radioimmunoassay was 0.99 (n = 63, p less than 0.001). Circulating thyroglobulin was detectable in 90% of 146 normal subjects, the concentration being 13.3 +/- 10.3 ng/ml (mean +/- S.D.). Interference of anti-thyroglobulin autoantibody with the assay for thyroglobulin was smaller than that in radioimmunoassay. 2) Another method using human thyroglobulin conjugated with beta-D-galactosidase and silicone rod coated with human thyroglobulin was developed for the measurement of circulating (anti-human thyroglobulin) autoantibody. The sensitivity of the assay with as little as 5 microliter of serum was 7 fmoles/tube corresponding to 220 ng/ml of serum, which was equal to or rather higher than that of radioimmunoassay. The highly significant correlation was observed between the concentrations of anti-thyroglobulin autoantibody determined by the present assay and a radioimmunoassay (r = 0.80, n = 74, p less than 0.001) and also between those by the present assay and those by tanned red cell hemagglutination (r = 0.78, n = 199, p less than 0.001). No effect of thyroglobulin on the present assay was observed unless the ratio of the amount of thyroglobulin to that of (anti-human thyroglobulin) immunoglobulin G was higher than a tenth.