An evaluation of serum thyroxine binding globulin as a routine test of thyroid function.

Serum thyroxine binding globulin (TBG) values were correlated with other thyroid function test results and with the clinical condition in 680 patients. The estimation of serum TBG was helpful in the evaluation of thyroid status only in those patients who were either acutely ill, were taking the contraceptive pill, or were pregnant. Further, the derived index, thyroxine: TBG ratio, proved to be a better diagnostic index than the thyroxine:tri-iodothyronine uptake ratio and in many cases would have avoided the use of more expensive and time-consuming tests.