Relationship Between Total Thyroxine and Absolute Free Thyroxine and the Influence of Absolute Free Thyroxine on Thyroxine Disposal in Humans¹

Abstract

Studies were conducted concerning the relation between TT4 and AFT4 in a family with TBG deficiency, consisting of 8 affected and 16 unaffected members, and in a group of 48 normals. A highly significant positive relationship between these 2 parameters was found within the family, as well as within the group of normals. Subjects with TBG deficiency had low TT4 and lowered AFT4 levels. From additional studies it appeared that there existed no relationship between AFT4 and T4 disposal in 20 euthyroid controls, including 2 subjects with TBG deficiency and 2 females with TBG elevation due to oral contraceptives. It is concluded that in these circumstances AFT4 was not a clear determinant in the absolute peripheral T4 turnover.