An Evaluation of the Perchlorate Discharge Test

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Abstract
Employing a modified technique which reduces the variability affecting the calculation of thyroid I131 content, 144 perchlorate discharge tests were performed upon normal persons and patients with abnormal thyroid function. In euthyroid patients the test was considered positive if the thyroid I131 content at 120 min (i. e., 57 min. after perchlorate administration) was lower than that at 60 min. and negative if it was unchanged or increased. In thyrotoxic patients a more reliable assessment could be made at 90 min. No discharge occurred in 24 euthyroid control subjects. However, positive discharge tests were observed in 59 of 82 euthyroid persons who had received a drug capable of inhibiting the organic binding of iodine by the thyroid. In 9 of 11 patients with untreated thyrotoxicosis the discharge test was negative, but positive values were recorded in 19 of 20 when carbimazole or carrier iodide had been administered. The time of administration of perchlorate was important, as shown in 4 subjects with impaired organic binding. When perchlorate was given at 4 or 6 hr. instead of 63 min. after the dose of I131, the discharge was much less evident. The test was also performed upon 7 normal persons 24 hr after the administration of TSH [thyroid stimulating hormone]. Thyroid I131 was not discharged. The perchlorate discharge test appears specific for demonstrating defective organic binding of iodine by the thyroid, and its value is enhanced by the increased sensitivity achieved by the technique described.