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Thyroxine, Free (Free T4)
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Ordering Recommendation
Not the preferred initial thyroid disorder screening test. Order following an abnormal thyroid stimulating hormone (TSH) result to diagnose thyroid disease. Order in conjunction with Thyroid Stimulating Hormone (0070145) in cases of suspected secondary hypothyroidism.
Mnemonic
Methodology
Quantitative Electrochemiluminescent Immunoassay
Performed
Sun-Sat
Reported
Within 24 hours
New York DOH Approval Status
Specimen Required
Serum separator tube or plasma separator tube. Also acceptable: Green (sodium or lithium heparin) or lavender (EDTA).
Allow specimen to clot completely at room temperature. Separate serum or plasma from cells ASAP or within 2 hours of collection. Transfer 1 mL serum or plasma to an ARUP Standard Transport Tube. (Min: 0.5 mL)
Refrigerated.
Grossly hemolyzed specimens.
After separation of cells: Ambient: 5 days; Refrigerated: 1 week; Frozen: 1 month
Reference Interval
Effective May 16, 2011
| Free Thyroxine, ng/dL | |
|---|---|
| 0-3 days | 0.7-2.7 ng/dL |
| 4-30 days | 0.8-3.1 ng/dL |
| 1-23 months | 0.5-2.3 ng/dL |
| 2-6 years | 0.9-1.8 ng/dL |
| 7-11 years | 0.9-1.7 ng/dL |
| 12-19 years | 0.9-1.6 ng/dL |
| 20 years and older | 0.8-1.7 ng/dL |
| Pregnancy, 1st Trimester | 0.9-1.4 ng/dL |
| Pregnancy, 2nd Trimester | 0.7-1.3 ng/dL |
Interpretive Data
FDA
Note
Hotline History
CPT Codes
84439
Components
| Component Test Code* | Component Chart Name | LOINC |
|---|---|---|
| 0070138 | Thyroxine Free | 3024-7 |
Aliases
- Free Thyroxine
- FT4, Serum
- Non-Protein Bound Tetraiodothyronine
- T4 Free, Serum
- T4, Free
- Thyroid Function Cascade
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