THYROXINE BINDING GLOBULIN (O.S)

Overview

The measurement of TBG can be used to establish the presence of TBG deficiency or excess suggested by abnormal Total serum T4 and T3 concentrations in the presence of normal free levels of these hormones. A change in thyroxine-binding globulin (TBG) concentration may be of hereditary, pathophysiologic, or pharmacologic origin. The TBG concentration indicates whether an abnormally high or low total thyroid hormone concentration is offset by a parallel increase or decrease in TBG concentration. In TBG deficiency, one may find euthyroid patients with extremely low total thyroxine (T4) values. Conversely, patients with high TBG levels may be clinically euthyroid with high serum total T4 values.