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Free T4 (Thyroxine)
Normal Reference Range
3.25 – 6.21 pmol/L
Test Information
A balanced blend of free and protein-bound T3 circulates in the blood. T3 is associated with albumin, thyroxine-binding globulin (TBG), and albumin.
Only 0.2-0.4% of the total T3 is present in the solution as unbound or free T3 (FT3) due to the binding of these proteins. The thyroid hormone that is physiologically active is represented by this free fraction. F T3 is often raised more than free thyroxine (FT4) in toxic adenomas and Graves' disease. Occasionally, in about 5% of people with hyperthyroidism (T3 thyrotoxicosis), free T3 levels are raised alone. In toxic multinodular, on the other hand, FT4 levels are raised more than free T3. To differentiate between these types of hyperthyroidism, serum-free is helpful.
Additionally, keeping an eye on hypothyroidism is helpful.
Clinical Indications
The diagnosis and management of thyrotoxicosis as well as differentiating the diagnosis of hyperthyroid disorders and to monitor the patient on tri-iodothyronine
Sample Required
5mL serum sample tube is required for the T3 blood test
Min. sample volume
1.0mL
Special Instructions and Precautions
Not applicable
Time Limits For Retrospective Testing
5 days
Any factors affecting the test
Not applicable
Turnaround Time
6 hrs
Referral centre (if applicable)
Not applicable
Test Code
FT4