Free T3 (free triiodothyronine)
| Category | Biochemistry |
|---|---|
| Test background |
T3 is more potent than T4 and both circulate in the blood as an equilibrium mixture of free and protein-bound hormone. T3 is bound to thyroxine binding globulin (TBG) and albumin. The free fraction, 0.2-0.4 % of the total T3, is present in solution as unbound or free T3 (FT3) and represents the physiologically active thyroid hormone. FT3 is typically elevated to a greater degree than free thyroxine (FT4) in Graves' disease and in toxic adenomas. Free T3 alone is elevated (T3 thyrotoxicosis) in about 5 % of the hyperthyroid population. |
| Clinical Indications |
Diagnosis and management of thyrotoxicosis |
| Reference range | 2.4 – 6.0 pmol/L |
| Sample & container required | SST (gold top) |
| Sample volume | 0.5 mL |
| Turnaround time | 1 day |