This article is from the Interpretation Of Lab Test Profiles, by Ed Uthman firstname.lastname@example.org with numerous contributions by others.
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