Thyroid
Free Thyroxine Index
%View
Thyroid
T4, Free (Direct)
Free T4 measures the amount of unbound thyroxine (T4) circulating in your blood—the form that’s available to convert into active T3. It reflects how well your thyroid is producing hormone, and how much is actually available for metabolic use. It’s more meaningful than Total T4 because it excludes the portion that’s bound to proteins and inactive. Free T4 is especially useful alongside TSH and Free T3 to assess thyroid function, conversion efficiency, and energy regulation.
- Unit
- ng/dL
- Health impacts
- Thyroid
In your dashboard
Your trend, against your optimal range.
Example data · how your trend would appear once you test
At every level
What we'd do at any value.
Exploring
1.45ng/dL
LowOptimal 1.10–1.80High
In your optimal zone
Habits that hold this position.
No specific guidance for this zone yet. We're working on it and will update this soon.
Order a test
Pick the lab that fits your day.
LabCorpTest code: 001974$14
QuestTest code: 866$14
BioreferenceTest code: 0091-9$18.98
Keep exploring