Intermediate
Technical
IVT
Free T4
The unbound, metabolically active fraction of thyroxine hormone measured in serum.
Full Definition
Free thyroxine (Free T4) represents the small percentage of thyroxine hormone that circulates unbound to proteins in the bloodstream. Unlike total T4, which includes both bound and unbound hormone, Free T4 provides a more accurate assessment of thyroid function as it reflects the hormone available for tissue uptake. This test is essential for diagnosing thyroid disorders and monitoring treatment effectiveness.
Usage
Usage note: Always capitalize 'Free' and use 'T4' not 'T-4' in medical contexts.
In Context
- "The patient's Free T4 level of 0.8 ng/dL falls within the normal reference range." — Laboratory report
- "Free T4 should be measured alongside TSH for comprehensive thyroid assessment." — Clinical guideline
Also known as
Free thyroxine
FT4
Contrasted with
Total T4
Bound T4
Don't confuse with
T3
Total T4
Reverse T3