Thyroxine-Binding Globulin (TBG), Serum
Use
Thyroxine binding globulin (TBG) is the high-affinity serum binding protein for thyroxine and triiodothyronine. It helps maintain a constant level of metabolically important free hormone by adjusting production based on TBG concentration. Elevated TBG levels can be influenced by factors such as pregnancy, genetic predisposition, oral contraceptives, and estrogen therapy. Decreased TBG levels may result from anabolic steroids, glucocorticoids, hypoproteinemic states, liver disease, nephrotic syndrome, and congenital TBG variants. This test is useful in cases where total thyroid hormone levels do not correlate with thyrometabolic status, especially during pregnancy or when using contraceptive steroids.
Special Instructions
The test can be useful in cases where total thyroid hormone levels do not correlate with thyrometabolic status, such as during pregnancy or with the use of contraceptive steroids. Patient should not take multivitamins or dietary supplements containing biotin 12 hours before specimen collection.
Limitations
Female individuals using estrogen-based contraception may exceed the reference range. Asfotase alfa, a recombinant form of alkaline phosphatase, can interfere with in vitro diagnostic assays using alkaline phosphatase detection systems. Patients using asfotase alfa should utilize a non-alkaline phosphatase methodology for testing.
FDA ApprovedNew York Approved
Methodology
Immunoassay (CLIA)
Biomarkers
LOINC Codes
- 3021-3
- 3021-3
Result Turnaround Time
1-3 days
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
0.5 mL
Minimum Volume
0.35 mL
Container
Plastic vial
Collection Instructions
Centrifuge and aliquot serum into a plastic vial.
Patient Preparation
For 12 hours before specimen collection, patient should not take multivitamins or dietary supplements containing biotin (vitamin B7).
Causes for Rejection
Reject due to gross hemolysis; OK for gross lipemia.
Stability Requirements
| Temperature | Period |
|---|---|
| Refrigerated | 7 days |
| Frozen | 30 days |