Iodine Balance Studies in Patients with Normal and Abnormal Thyroid Function

Iodine balance studies are reported in patients with normal and abnormal thyroid function. Intake of iodine was constant during the balances, which were carried out in a metabolic ward. Difficulties and sources of error in fecal iodine measurement are discussed. In 8 euthyroid individuals on an intake of iodine of approximately 100 μg/day, fecal excretion of iodine averaged 15.0 μg/day (range 3–31 μg/day). Six of these individuals were in positive iodine balance. In 5 patients with thyrotoxicosis, fecal iodine levels were significantly higher, with a mean of 37.2 μg/day (range 22–72 μg/day), but only one patient was in markedly negative balance. In 2 patients with nontoxic goiter, thought to be due to iodine deficiency, a strongly positive iodine balance was observed. In 3 patients with hypothyroidism, fecal excretion of iodine was low. The evidence that fecal iodine is principally derived from endogenous thyroid hormone is discussed. It is suggested that fecal losses of iodine may result in a low level o...