Calculation of an estimate of throxine-binding globulin capacity

An estimate of the serum thyroxine-binding globulin (TBG) may be computed from determinations of serum thyroxine and triiodothyronine uptake. A general equation for this computation is presented and a computer program for the calculation of the estimating parameters is dicussed. With these methods, the regression equation for the calculated TBG and the observed TBG is the line of identity, and the correlation coefficients from determinations on data from two laboratories were +0.88 and +0.96. The calculated TBG may be used as a screening test for abnormalities of thryoxinebinding protein and as an aid in the proper interpretation of thyroid function studies.