T3 Uptake

Thyroid function test for the diagnosis of hypothyroidism or hyperthyroidism, used with thyroxine (T₄) or equivalent to provide free T₄ index, FTI. An indirect measure of binding protein, the T₃ uptake reflects available binding sites (ie, reflects TBG). T₃ uptake is not a measurement of serum T₃. It should never be used alone; rather, its usual application is use with thyroxine (T₄).