title: A numerical comparison of the use of T3-uptake values and of TBG levels for the estimation of free thyroxine in serum.
abstract: The correlation of the diagnostic indices FTI and T4/TBG with actual free T4 levels (FT4) was investigated by numerical analysis. It was shown that, FT4 being kept constant, both indices vary with altered TBG concentrations. Thus neither index is truly proportional to FT4. In this respect both indices appear doubtful tools for diagnosing patients with abnormal TBG levels. A "map" constructed by plotting T4 versus T3U appeared to offer a higher discriminatory potential with respect to pathologic FT4 values. Such an idealized map was shown to consist of hypo-, eu- and hyperthyroid domains separated by lines governed by the limit values of the FT4 normal range. In practice, of course, these domains are separated by border regions rather than border lines and they should be derived from clinical data.
mesh_terms: D001665:Binding Sites; D003201:Computers; D006801:Humans; D006980:Hyperthyroidism / Q000175:diagnosis; D007037:Hypothyroidism / Q000175:diagnosis; D008433:Mathematics; D013974:Thyroxine / Q000097:blood*; D013975:Thyroxine-Binding Proteins / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*
chemical_list: D013975:Thyroxine-Binding Proteins; D014284:Triiodothyronine; D013974:Thyroxine