Significance of the Iodide-Perchlorate Discharge Test in Patients with131I-Treated and Untreated Hyperthyroidism

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Abstract
Our previous study of the iodide-perchlorate test in patients with Hashimoto's thyroiditis led to us to assess the significance of the test in patients with Graves' disease. Perchlorate tests were performed by a conventional method (ClO4 test) and a modified technique in which a dose of 250 or 500 μg 127I was added to the tracer 131I (I-ClO4 test). In the I-ClO4 test (500 μg 127I), a significant discharge was observed in the thyrotoxic patients, as well as in the patients rendered euthyroid by 131I treatment. With the smaller dose of 127I (250 μg), only 131I-treated patients showed significant iodide-perchlorate discharge. The magnitude of dischargeability (discharge percent) in the 131I-treated patients was greater than in thyrotoxic patients. ClO4 tests were negative in both the thyrotoxic and 131I-treated euthyroid patients. Chronic treatment with iodide induced hypothyroidism in 5 of 7 euthyroid patients who had been treated with 131I. The ClO4 test was negative in all patients except one, whereas the I-ClO4 test was positive in 6 of 7 patients. It would appear that the susceptibility of patients with Graves' disease to acute and chronic iodide loads may be enhanced after 131I treatment, presumably by impairment of the thyroidal organic binding mechanism. The latter is more frequently detectable by the iodide-perchlorate test.

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