Age- and sex-related differences of serum thyroxine binding globulin (TBG) in healthy subjects.

Serum concentrations of thyroxine binding globulin (TBG) were measured in healthy adult subjects aged 20-79 years (152 males and 148 females) by radioimmunoassay. In contrast to previous reports, there were no significant age-related differences in either sex. Significant sex-related differences were observed only in the fourth decade, being higher in females than males (P less than 0.01).