Abstract
The present report deals with the measurement of serum thyroglobulin (Tg) in various thyroid disorders by using radioimmunoassay (RIA). The results were as follows :
1) A specific and simple solid-state RIA for the measurement of Tg in human serum was used. This system was a direct RIA using plastic cups coated with crude anti-thyroglobulin antibodies (anti-Tg) and 125I labeled purified anti-Tg. The purification of anti-Tg was performed by affinity chromatography using Tg-Sepharose, as an immunoadsorbent.
2) Affinity chromatography was carried out using a modification of the method of Cuatrecasas. The immunoadsorbent (Tg-Sepharose conjugate) was used in a column procedure for the isolation of anti-Tg from globulin fractions obtained from Hashimoto's sera. The elution was performed with 4M NaI or 0.17 M Glycine-HCl with pH 2. 3. The eluted materials contained a very small amount of Tg which was removed by Sephadex G-200 chromatography using the same elution buffer. The high purity of the anti-Tg obtained was demonstrated by the fact that almost all of the final product was bound with Tg by using Sephadex G-200 chromatography.
3) A direct RIA consisting of two incubation steps was applied for Tg measurement. During the first incubation, standard Tg or Tg in serum was bound to the antibody coated cup. After washing, equal amounts of radioactive purified anti-Tg were incubated with the bound Tg. The cups were then washed again, and counted separately. The radioactive counts thus obtained, increased with the amounts of Tg bound to the anti-Tg by the first incubation.
The sensitivity of the assay was 4 ng/ml. T3 and T4 did not cross-react against Tg, and did not interfere with the binding between Tg and 125I-anti-Tg. A dilution curve was constructed using the serum of a patient with Graves' disease ; the post-operative serum contained a very high level of Tg. This curve paralleled the standard curve. By adding constant Tg to a normal serum or Graves' serum, Tg recovery was good. However, in regard to Hashimoto's serum, Tg recovery was unsatisfactory.
4) Serum Tg concentrations were measured in patients with various thyroid disorders. Tg was detectable in 60% of 25 normal subjects tested, with an average level of 26.5±26.5 (mean±SD) ng/ml. Serum concentrations in 23 simple goiter, 9 untreated Graves' disease, 27 treated Graves' disease, 10 Hashimoto's thyroiditis having undetectable anti-Tg, 13 adenoma and 8 thyroid cancer were measured as 37.9±87.0ng/ml, 324.3±517.8 ng/ml, 71.0±138.6 ng/ml, 172.5±314.5 ng/ml, 126. 0±146.0 ng/ml and 15.0±14.1 ng/ml, respectively. In two patients with subacute thyroiditis, one patient had 100 ng/ml and the other gave a value of 280 ng/ml.
In patients with Graves' disease, there was no correlation between Tg concentration and T3 and T4. In two patients with Graves' disease undergoing partial thyroidectomy, serum Tg levels went up 16-30 μg/ml after the surgery. A patient with thyroid cancer showed a serum Tg value of 350 ng/ml after total thyroidectomy.
5) High Tg levels were observed mostly in patients with low titers of anti-Tg. However, even with the existence of potent anti-Tg, Tg could be detected in some instances. It seemed that these Tg values represented free Tg concentration when used in the present direct RIA system.
