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Thyroxine, Free
Test CodeFT4
Alias/See Also
Free T4, FT4
CPT Codes
84439
Preferred Specimen
Plasma Light GREEN (PST)
Other Acceptable Specimens
Serum (RED) or GOLD (SST)
Instructions
No hemolysis.
Allow serum samples to clot completely before centrifugation.
Within two hours after centrifugation, transfer cell-free sample to a storage tube. Tightly stopper the tube immediately.
Allow serum samples to clot completely before centrifugation.
Within two hours after centrifugation, transfer cell-free sample to a storage tube. Tightly stopper the tube immediately.
Specimen Stability
- Store samples tightly stoppered at room temperature (15 to 30°C) for no longer than eight hours.
- If the assay will not be completed within eight hours, refrigerate the samples at 2 to 8°C.
- If the assay will not be completed within 48 hours, or for shipment of samples, freeze at -20°C or colder. Thaw samples only once.
Setup Schedule
24x7
Reference Range
0.60-1.60 ng/dL
Interpretations
Results from patient samples with diagnosed disease states gave:
Interpretations
Results from patient samples with diagnosed disease states gave:
| Category | FT4 (ng/dL) |
| Hypothyroid | <0.60 |
| Hyperthyroid | >1.60 |
| Euthyroid | 0.60-1.60 |
Clinical Significance
Free thyroxine (free T4) tests are used to help evaluate thyroid function and diagnose thyroid diseases, including hyperthyroidism and hypothyroidism, usually after discovering that the thyroid stimulating hormone (TSH) level is abnormal.
T4 and another hormone called triiodothyronine (T3) are produced by the thyroid gland. They help control the rate at which the body uses energy and are regulated by a feedback system. TSH stimulates the production and release of T4 (primarily) and T3 from the thyroid gland.
Performing Laboratory
CRMC Laboratory
CCMC Laboratory
