Thyroxine, Free (Free T4)
Also known as: FT4
Use
This test measures the level of free thyroxine (Free T4) in the blood, which is important for evaluating thyroid function and diagnosing thyroid disorders. It is particularly useful following an abnormal thyroid stimulating hormone (TSH) result to diagnose thyroid disease and in cases of suspected secondary hypothyroidism, where it is ordered in conjunction with TSH. Free T4 is the unbound form of thyroxine and provides a more accurate indication of thyroid hormone status than total T4, which includes both bound and unbound hormone.
Special Instructions
Not provided.
Limitations
The test may not be suitable for patients with altered binding protein levels, as this can affect the measurement of free thyroxine. Grossly hemolyzed specimens are unacceptable and should be rejected. It is important to maintain proper storage temperatures and timelines to prevent degradation of the sample, which may affect test results. Free T4 levels can be affected by a variety of factors including illness, medications, and pregnancy, which should be considered when interpreting results.
FDA ApprovedNew York Approved
Methodology
Immunoassay (Electrochemiluminescent)
Biomarkers
Thyroxine Free
Analyte
LOINC Codes
- 3024-7 - T4 Free SerPl-mCnc
Result Turnaround Time
0-1 day
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
1 mL
Minimum Volume
0.5 mL
Container
Serum separator tube or plasma separator tube. Also acceptable: Green (lithium heparin), lavender (K2EDTA or K3EDTA), or pink (K2EDTA).
Collection Instructions
Allow specimen to clot completely at room temperature. Separate serum or plasma from cells ASAP or within 2 hours of collection.
Storage Instructions
Refrigerated.
Causes for Rejection
Grossly hemolyzed specimens
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 5 days |
| Refrigerated | 7 days |
| Frozen | 1 month |
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