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| A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # |
T4, Free
Test CodeFT4
Alias/See Also
Free Thyroxine, FT4, Free T4
Preferred Specimen
1.0 mL plasma (0.5 mL minimum)
Transport Container
PST (light green top). Red top and SST also acceptable
Specimen Stability
Room temperature: 24 hours, Refrigerated: 14 days, Frozen: 30 days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Grossly hemolyzed specimens are unacceptable.
Limitations
"The following substances can cause elevated FT4 results by releasing T4 from serum binding protein:
Carbamazepine, Furosemide, Ibuprophen,Phenytoin, Salicylic acid, Valproic acid"
Carbamazepine, Furosemide, Ibuprophen,Phenytoin, Salicylic acid, Valproic acid"
Reference Range
| Age | Male | Female |
| Adult (>18 years): | 0.76 – 1.46 ng/dL | 0.76 – 1.46 ng/dL |
| Pediatric: | ||
| 0 - 3 days | 0.97 - 1.87 | 0.93 – 1.44 |
| 4 - 30 days | 0.78 - 1.52 | 0.81 – 1.44 |
| 1 - 11 months | 0.89 - 1.48 | 0.93 – 1.40 |
| 1 - 5 years | 0.97 – 1.25 | 1.01 – 1.32 |
| 6 - 10 years | 0.93 – 1.32 | 0.93 – 1.25 |
| 11 - 15 years | 0.97 – 1.25 | 0.89 – 1.20 |
| 16 - 18 years | 0.97 – 1.25 | 0.93 - 1.25 |
Clinical Significance
"Thyroxine is synthesized in the thyroid gland and once in the circulation, almost all thyroxine (99.97%) is protein bound. It is only the 0.03% unbound or “free thyroxine” that is capable of binding cellular receptors resulting in a physiologic response.
FT4 concentrations more closely parallel thyroid dysfunction in patients with either hypo- or hyperthyroidism than do the serum levels of total thyroxine."
FT4 concentrations more closely parallel thyroid dysfunction in patients with either hypo- or hyperthyroidism than do the serum levels of total thyroxine."
