T3 Uptake

Test ID:

704289

CPT code:

84479

Synonyms:

Thyroid Hormone-binding Ratio (THBR)

Clinical Use:

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

Specimen Type:

Serum

Requested Volume:

1 mL (adult), 0.8 mL (pediatric)

Minimum Volume:

0.5 mL (adult), 0.3 mL (pediatric)

Container Type:

Red-top tube or gel-barrier tube

Patient Preparation:

It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.