IMPORTANT NOTE: T3 uptake is not a measurement of serum T3. It should never be used alone; rather, its usual application is use with thyroxine (T4).

Synonyms: T3 Resin Uptake; Thyroid Hormone Binding Ratio (THBR)

Why It Is Done

This test is used to evaluate thyroid function and screen for hyperthyroidism. It is usually ordered when a patients TSH or T4 test comes back abnormal or when a patient has signs of hyperthyroidism.

Test Overview

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).

How To Prepare

No special preparation needed.