[Frequency distribution of an index for free thyroxin in relation to age and thyroid status].

We compared an index for free thyroxine (FT4I) between groups of patients which were formed according to the results of radioiodine testing. An elevation of free thyroxine (as measured by the FT4I) which has been reported in elderly women by other authors could not be confirmed. Overlapping between euthyroidism and hyperthyroidism was not found as disturbing as reported elsewhere, a finding which can probably be explained by the different criteria for the categories "euthyroidism" and "hyperthyroidism". A group with depressed radioiodine uptake had an unexpected high percentage of elevated FT4I. These cases may be explained as toxic goitres. The incidence of hypothyroidism (as judged by FT4I) in this group is low compared with the incidence of obvious exogenous exposure to excessive iodide. Cases presenting with a normal radioiodide uptake together with absent suppression by thyroxine administration are more often connected with a normal FT4I and are therefore believed to be euthyroid; less frequently they are truly hyperthyroid (FT4I). In patients previously treated with radioiodine an elevated FT4I is found suprisingly often. A reevaluation of the radioiodine dosage and the course of the disease in these numerous patients seems to be indicated.