[Thyroxine-binding globulin (TBG). Clinical studies on the regulation of TBG concentration in serum and the value of TBG for the evaluation of thyroid function].

: 1. The radioimmunoassay (RIA) and the competitive ligand binding assay (CLBA) are convenient routine methods for the precise and reproducible measurement of TBG in large numbers of serum samples. 2. There is an age dependent variation of the TBG-concentration in serum. There is a steady decrease of TBG with increasing age with a minimum between the 20th and 50th year. In higher age TBG increases again significantly. 3. There are significantly negative correlation between TBG-serum levels on the one hand and free T4- and T3- fractions on the other. The low TBG-level in hyperthyroid patients increases gradually to normal during treatment with thyroid blocking drugs, the elevated TBG-concentrations in hypothyroid patients decrease to normal during treatment with thyroid hormones. 4. Estrogen stimulates TBG-synthesis in the liver. During enhanced endogenous estrogen production (pregnancy) as well as during exogenous estrogen application a rise occurs in TBG-concentration in serum, which seems to be dose related. 5. Androgens induces a decrease of the TBG-concentration in serum. 6. During viral hepatitis and in compensated cirrhosis of the liver TBG-concentration is significantly elevated. In cirrhosis of the liver with poor hepatic function the TBG-concentration is decreased. 7. The T4/TBG-quotient is a good parameter to estimate free T4-concentration in serum.