Clinical value of the plasma butanol-extractable (thyroxine) I131 in the diagnosis of hyperthyroidism and myxedema.

THYROXINE has been accepted generally as the major active hormone of the thyroid gland. It can be separated from nonthyroxine protein-bound iodine and inorganic iodine in plasma by extraction with butyl alcohol (1–4). Radioactive iodine (I131) is incorporated into the thyroxine molecule by the thyroid gland, and the labeled thyroxine can be recovered in the butanol-extractable fraction of the plasma protein-bound iodine (4–6). It is of interest to determine whether or not the rate of formation and release of thyroxine tagged with I131 has special value in the diagnosis of hyperthyroidism and myxedema. The present study was undertaken therefore to evaluate the plasma butanol-extractable I131 as a clinically useful measure of thyroid function and to compare it with the plasma proteinbound I131. METHODS AND MATERIALS Testing procedures Studies were conducted on 50 euthyroid hospital patients, 12 patients with moderate or severe hyperthyroidism, and 5 patients with primary myxedema. None of the euthyroid subj...