[T3-thyrotoxicosis: incidence, significance and correlation with iodine intake]

In a part of patients with thyrotoxicosis the serum triiodothyronine concentration increases only while free thyroxin level remains in the normal range (T3-thyrotoxicosis). This condition occurs in patients with untreated or treated thyrotoxicosis and in some other but rare thyroid disease, respectively. In this study occurrence and importance of T3-thyrotoxicosis were discussed. This form occurred in 11% of untreated thyrotoxicosis (53/480). The majority of patients suffering from T3-thyrotoxicosis have autonomous thyroid function (i.e. toxic uninodular and multinodular goiter: 45/53, 85%). In case of suppressed TSH and normal free thyroxin T3-thyrotoxicosis can be expected in 40% (53/140). The rate of free-triiodothyronin elevation is highest in Graves' disease with autoimmune origin. We consider the possibilities of development of triidothyronine increasing and the importance of iodine deficiency. Our patients are living in an area where mild iodine deficiency can be proved on the basis of decreased iodine excretion in urine. The results show the diagnostic importance of free-T3 determination.