Radioiodine turnover studies as a means to predict stable intrathyroidal iodine stores and comments upon its use in the diagnosis and treatment of hyperthyroidism.

Stable intrathyroidal iodine pool (ITI) is known to affect both diagnosis and treatment of hyperthyroidism. Very few laboratories have facilities to measure ITI. In our department x-ray fluorescence was routinely used for more than 15 years. We report here that it is possible to predict the ITI by means of classic 131I turnover studies and at least distinguish hyperthyroid patients with a small ITI pool ("small pool" patients) from those with a large ITI. It could be shown from a retrospective study (selected hyperthyroid patients, n = 118) that (1) in our area the small pool patients represent the majority as opposed to the situation in the United States, (2) that there was a highly significant negative correlation (p < 0.001) between the PB 131I at 24 h and ITI, and (3) that the non-small pool patients were more resistant to treatment than the others. In a prospective study of 91 consecutive patients with a thyroid problem, it was be shown that in the euthyroid group no correlation could be found between ITI on the one hand and 131I uptake and PB 131I at 24 h or urinary iodine on the other. In the hyperthyroid patients a strong negative correlation was again found between ITI and PB 131I (p < 0.001), stronger than with 131I uptake p = 0.093). No correlation existed with urinary iodine. In a second prospective study of hyperthyroid patients (n = 56), it was confirmed that measuring the PB 131I could classify hyperthyroid patients into non-small pool and small pool subjects.(ABSTRACT TRUNCATED AT 250 WORDS)