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 diagno sis and treatment of hyperthyroidism. Very few laboratories have facil ities to measure ITI. In our department x-ray fluorescence was routine ly used for more than 15 years. We report here that it is possible to predict the ITI by means of classic I-131 turnover studies and at leas t distinguish hyperthyroid patients with a small ITI pool (''small poo l'' patients) from those with a large ITI. It could be shown from a re trospective study (selected hyperthyroid patients, n = 118) that (1) i n our area the small pool patients represent the majority as opposed t o the situation in the United States, (2) that there was a highly sign ificant negative correlation (p < 0.001) between the (PBI)-I-131 at 24 h and ITI, and (3) that the non-small pool patients were more resista nt to treatment than the others. In a prospective study of 91 consecut ive patients with a thyroid problem, it was be shown that in the euthy roid group no correlation could be found between ITI on the one hand a nd I-131 uptake and (PBI)-I-131 at 24 h or urinary iodine on the other . In the hyperthyroid patients a strong negative correlation was again found between ITI and (PBI)-I-131 (p < 0.001), stronger than with I-1 31 uptake p = 0.093). No correlation existed with urinary iodine. In a second prospective study of hyperthyroid patients (n = 56), it was co nfirmed that measuring the (PBI)-I-131 could classify hyperthyroid pat ients into non-small pool and small pool subjects. It is suggested tha t the (PBI)-I-131 at 24 h should be reintroduced routinely in the work up of hyperthyroid patients.