Hyperthyroidism induced by potassium iodide given in the course of 125I-fibrinogen test

Hyperthyroidism developed in three patients during the administration of potassium iodide given for the purpose of blocking the thyroid uptake of radioactive iodine liberated in the course of the 125I-fibrinogen test. In a consecutive series of 31 geriatric patients, who received potassium iodide for the same reason, biochemical hyperthyroidism developed in three instances and significant depression of thyroid function was observed in 10. The performance and the interpretation of the 125I-fibrinogen test are unaffected if iodide is not administered to the patient. The possible hazards to some patients of either induced hyperthyroidism or faulty assessment of thyroid function may be greater than the risk of thyroid irradiation. It is suggested that for the performance of the 125I-fibrinogen test potassium iodide need not be given to the elderly and should be given in a dose of 30 mg daily for two weeks to younger patients. Under certain circumstances potassium perchlorate may be a preferable drug for preventing the accumulation of radioactive iodine by the thyroid.