This test measures the amount of thyroxine-binding globulin (TBG) in the patient's serum. When TBG is increased, T3 uptake is decreased, and vice versa. T3 Uptake does not measure the level of T3 or T4 in serum. Increased T3 uptake (decreased TBG) in euthyroid patients is seen in chronic liver disease, protein-losing states, and with use of the following drugs: androgens, barbiturates, bishydroxycourmarin, chlorpropamide, corticosteroids, danazol, d-thyroxine, penicillin, phenylbutazone, valproic acid, and androgens. It is also seen in hyperthyroidism. Decreased T3 uptake (increased TBG) may occur due to the effects of exogenous estrogens (including oral contraceptives), pregnancy, acute hepatitis, and in genetically determined elevations of TBG. Drugs producing increased TBG include clofibrate, lithium, methimazole, phenothiazines, and propylthiouracil. Decreased T3 uptake may occur in hypothyroidism