T4 (Thyroxine), Total and Free, Serum
Use
Assessing thyroid function when thyroid function disorders are suspected. Measurement of total T4 gives a reliable reflection of clinical thyroid status in the absence of protein binding abnormalities. Free thyroxine comprises a small fraction of total thyroxine. The free T4 (FT4) is available to the tissues and is, therefore, the metabolically active fraction. Elevations in FT4 cause hyperthyroidism, while decreases cause hypothyroidism.
Special Instructions
This test is particularly useful in detecting conditions related to thyroid dysfunction. Elevations in FT4 indicate hyperthyroidism, whereas decreases can signal hypothyroidism.
Limitations
Some individuals may develop antibodies that interfere with immunoassays, such as human anti-mouse antibodies (HAMA) or antibodies to streptavidin or ruthenium, which can interfere with the assay. It is important to correlate laboratory results with clinical findings.
FDA ApprovedNew York Approved
Methodology
Immunoassay (Electrochemiluminescence Immunoassay)
Biomarkers
LOINC Codes
- 90224-7
- 83122-2
- 83119-8
Result Turnaround Time
1-2 days
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
1 mL
Minimum Volume
0.625 mL
Container
Plastic vial
Collection Instructions
Centrifuge and aliquot serum into a plastic vial.
Causes for Rejection
Gross hemolysis or gross icterus
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 72 hours |
| Refrigerated | 7 days |
| Frozen | 30 days |