T UPTAKE

Test:
307
CPT:
84479
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Synonyms
Thyroid Hormone-binding Ratio (THBR), T3 Uptake
Special Instructions
This test reflects assessment of thyroxine-binding globulin (TBG) and should not be ordered alone. This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). 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.
Expected Turnaround Time
Within 1 day

Specimen Requirements

Specimen
Within 1 day
Volume
1 mL (adult), 0.8 mL (pediatric)
Minimum Volume
0.7 mL (adult), 0.3 mL (pediatric) (Note: This volume does not allow for repeat testing.)
Container
Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube. Do not use oxalate, EDTA, or citrate plasma.
Collection
If a red-top tube or plasma is used, transfer separated serum or plasma to a plastic transport tube.
Storage Instructions
Room temperature
Causes for Rejection

Test Details

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 (T4).

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