T3 Uptake
Also known as: Thyroid Hormone-binding Ratio (THBR)
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).
Special Instructions
This test reflects assessment of thyroxine-binding globulin (TBG) and should not be performed in isolation. Patients consuming high doses of biotin (vitamin B7/B8) should stop consumption at least 72 hours prior to sample collection to avoid interference.
Limitations
Alterations in TBG binding capacity can occur with major illness, high doses of salicylates and corticosteroids, and use of certain drugs such as heroin, methadone, phenytoin, and perphenazine. Although TBG alterations may occur due to malnutrition, metastatic malignancy, and abnormal serum protein patterns, such as nephrotic syndrome or cirrhosis, they also occur with physiological states like infancy, acromegaly, pregnancy, and influence from oral contraceptives and exogenous hormones, including androgens, steroids, and estrogens. There are also hereditary variations in TBG levels.
Methodology
Immunoassay (ECLIA)
Biomarkers
LOINC Codes
- 3050-2
- 3050-2
Result Turnaround Time
1 day
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
1 mL (adult), 0.8 mL (pediatric)
Minimum Volume
0.7 mL (adult), 0.3 mL (pediatric)
Container
Red-top tube, gel-barrier tube or green-top (lithium heparin) tube
Collection Instructions
If a red-top tube or plasma is used, transfer separated serum or plasma to a plastic transport tube.
Patient Preparation
Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.
Storage Instructions
Room temperature
Causes for Rejection
Do not use oxalate, EDTA or citrate plasma.
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 14 days |
| Refrigerated | 14 days |
| Frozen | 14 days |