A variant
albumin with abnormally increased
thyroxine-binding affinities has been identified, and termed as
familial dysalbuminemic hyperthyroxinemia (FDH). The aims of this study are to seek for a method of diagnosis to distinguish FDH from other causes of
hyperthyroxinemia and to investigate the nature of this abnormal
albumin. Percent T4 bound to
albumin was high in FDH, ranging 29-48% (normal range 3-8%), as measured in [125I] T4 loaded serum using a single immunoprecipitation by anti-
human albumin antibody. A subject with T4
autoantibody in serum had a lower value. Only a single subject with
TBG deficiency had an overlapped value (33%) with that of FDH, but the level of serum T4 could differentiate
TBG deficiency from FDH. Isoelectric focusing (IEF) showed a distint
albumin band with an isoelectric point of pH 5.05 in all FDH subjects, and this band was not compatible with any of 4
albumin bands seen in normals. These data suggest that only two simple measurements including the level of serum T4 and the single immunoprecipitation for [125I] T4-bound
albumin can distinguish FDH from other causes of
hyperthyroxinemia.