CHANGES IN BLOOD IODINE FRACTIONS AND RADIOACTIVITY UNDER THERAPY*†

Abstract

Changes in blood iodine fractions and radio-activity were studied in 23 patients under conservative therapy with radioactive iodide (I131). Both stable I and the radioactive isotope were studied continuously in the breath, body tissues, thyroid gland, and serum. The serum I was separated into organic and inorganic fractions. Thyroid function was appraised from (a) the thyroid clearance and (b) the thyroxine metabolic turnover rate (TMR). If overwhelming doses of radioiodide (I131) are avoided, the functional status of the human thyroid gland is not appreciably altered during the first week after conservative therapeutic dosage with the isotope. The thyroid clearance is the same as found in untreated glands; and the thyroxine metabolic turnover rate (TMR) is the same as found with test doses. Consequently test doses of I131 afford a reliable preview of the fate of conservative therapeutic doses over a wide range of thyroid activity.