T4, FREE
- Code
- 600.3500
- Name
- T4, FREE
- Category
- None
- Department
- Chemistry
- Start Date
- Expiration Date
- Synonyms
- FT4; Thyroxine, Free
- CPT Codes
- 84439
- Site
- Main Lab
- Reference Test
Specimen Information
- Type
Gold, SST
- Volume
1.5 ml
- Transport Info
Refrigerated
- Fasting Required?
- False
- Patient Instructions
- Reference Range
0.4 - 5.9 ng/dL
- Methodology
Fluorescence Polarization Immunoassay (FPIA)
Clinical Significance
The determination of free thyroxine is an important element in clinical routine diagnostics. Free T4 is measured together with TSH when thyroid function disorders are suspected. The determination of FT4 is also suitable for monitoring thyrosupressive therapy.
The thyroid hormone thyroxine (T4) is physiologically part of the regulating system of the thyroid gland and has an effect on general metabolism. The major fraction of the total thyroxine is bound to transport proteins (TBG, prealbumin and albumin). The free thyroxine (FT4) is the physiologically active thyroxine component.The determination of free T4 has the advantage of being independent of changes in the concentrations and binding properties of the binding proteins; additional determination of a binding parameter (T-uptake, TBG) is therefore unnecessary.