An Unusual Iodinated Protein of the Serum in Hashimoto’s Thyroiditis*

Protein-bound iodine may exist in forms other than thyroxine. Man and associates (1) found that patients receiving Lugol’s solution usually had a significant amount of serum iodine that was precipitable together with proteins (therefore not being inorganic iodide) but was not soluble in butanol (therefore not being thyroxine). Danowski and coworkers (2) made the same observations on rats given iodides or iodine. Robbins and associates (3, 4) have identified thyroglobulin in the serum after therapy with radioiodine (doses of 7 to 241 millicuries). This component was found in only small amounts in the serum of patients treated for hyperthyroidism; however, in about half the patients who had malignant lesions of the thyroid, a portion of the radioiodine precipitated along with proteins was identified as thyroglobulin.