Hyperthyroidism; diagnosis by failure of triiodothyronine to suppress uptake of iodine 131.

Sixty patients with abnormally high I(131) uptake were treated with liothyronine (L-triiodothyronine) for seven or eight days and then tested again. Fifty-five patients showed a suppression of iodine uptake sufficient to eliminate the possibility of hyperthyroidism. Also the therapeutic trial of liothyronine indicated whether they were euthyroid, or hypothyroid with iodine deficiency. Six of the patients showed insignificant change in the I(131) uptake after treatment with thyroid hormone-that is, the change from the original uptake was less than 30 per cent. These six patients were later confirmed to be hyperthyroid. In four patients the uptake at the second test was less by between 35 and 52 per cent than at the first. These four patients, like the remainder with even greater suppression in thyroid uptake, remained clinically euthyroid.The repeat I(131) uptake test was thus seen to be considerably more accurate than the single test and well worth the time required to perform it.