The T4/TBG ratio and the investigation of thyroid function.

The relationship between serum thyroxine (T4) and thyroxine-binding globulin (TBG) has been studied in "euthyroid" subjects. The T4/TBG ratios in these subjects has been calculated and compared with those found in patients suffering from myxoedema and thyrotoxicosis. The ratio allows a more precise selection of the borderline cases requiring Thyroid Stimulating Hormone and triiodothyronine assays, particularly when the serum TBG is raised or lowered.